the fishes of the nam theun and xe bangfai drainages, laos...the diversity of inland fishes in...

Hydroécol. Appl.© EDF, 2015DOI: 10.1051/hydro/2015005

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The fishes of the Nam Theun and Xe Bangfai drainages,Laos

Les poissons des bassins de la Nam Theun et de la Xe Bangfai,Laos

M. Kottelat

Aquatic biodiversity specialist, rue des Rauraques 6, 2800 Delémont, [email protected]

Abstract – The fish diversity of the Nam Theun and Xe Bangfai drainages was surveyedbetween 1996 and 2012. 74 species are now recorded from the Nam Theun and 178 fromthe Xe Bangfai drainages. Twenty-one (28%) of the Nam Theun species are endemic and 9(5%) of the Xe Bangfai species. At the time of the respective surveys, 54 species were newrecords for Laos, and 25 species were new to science. While the fish fauna of Xe Bangfai issimilar to that of the other main tributaries of the Mekong in Laos, the fish fauna of the NamTheun is characterised by a great proportion of endemics, several of which have affinities withspecies known from the opposite slope of the Annamite Range, in Vietnam. Besides, workconducted in relation with aquatic biodiversity surveys for the Nam Theun 2 project resultedin an increase of the fish fauna of Laos from 210 to 481 in 3 years between March 1996 andJune 1999 and the discovery of 128 species new to science and lead to the publication of anidentification guide. Specific studies have been conducted to assess the status of some ofthe endemic species that were potentially threatened by the Nam Theun 2 scheme: Sca-phognathops theunensis (still observed in 2012 downstream of Nakai Dam), Tor ater (mainlyrestricted to streams upstream of the reservoir), and Oryzias sp. 'swamp' (along the fringeof the reservoir). The status of the bitterling Rhodeus laoensis and its associated mussel isstill not clear. Most of the species endemic to the Nam Theun drainage are known upstreamof the reservoir, which is a protected area. The endemic species known on Nakai Plateau anddownstream of the dam are more at risk and require closer monitoring.

Key words – fish diversity, Mekong tributaries, endemism, hydropower project

Résumé – La diversité ichtyologique des bassins de la Nam Theun et de la Xe Bangfai a étésuivie entre 1996 et 2012. 74 espèces sont maintenant recensées pour le bassin de la NamTheun et 178 pour le bassin de la Xe Bangfai. Vingt-et-une (28 %) des espèces de la NamTheun y sont endémiques et 9 (5 %) de celles de la Xe Bangfai. Au moment des inventairesrespectifs, 54 espèces ont été ajoutées à la liste des espèces connues au Laos, et 25 espècesétaient nouvelles pour la science. Alors que la faune ichtyologique de la Xe Bangfai est similaireà celle des autres principaux affluents du Mékong au Laos, la Nam Theun est caractérisée

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2 M. Kottelat

par une grande proportion d’espèces endémiques, plusieurs de ces espèces présentant desaffinités avec les espèces connues du versant opposé de la chaîne annamitique, au Vietnam.Deplus, les travaux d'inventaire de labiodiversité aquatiqueconduitsen relation avec le projetde Nam Theun 2 ont fait passer la faune ichtyologique du Laos de 210 à 481 espèces en3 ans entre mars 1996 et juin 1999 ; ils ont mené à la découverte de 128 espèces nouvellespour la science et à la publication d'un guide d'identification. Des études spécifiques ont étéconduites afin d’évaluer le statut de quelques espèces endémiques potentiellement mena-cées par le projet hydroélectrique de Nam Theun 2 : Scaphognathops theunensis (encoreobservée à l’aval du barrage en 2012), Tor ater (restreinte principalement aux affluents enamont du réservoir), et Oryzias sp. 'swamp' (sur les bords du réservoir). Le statut de la bou-vière Rhodeus laoensis et de la moule associée à son cycle biologique n’est pas encore cla-rifié. La plupart des espèces endémiques de la Nam Theun sont connues en amont duréservoir, qui est une zone protégée. Les espèces endémiques connues du plateau de Nakaiet en aval du réservoir sont plus menacées et nécessitent un suivi attentif.

Mots clés – diversité ichtyologique, affluents du Mékong, endémisme, projet hydroélec-trique

1 INTRODUCTION

The diversity of inland fishes inSoutheast Asia is very high, with about3000 named species (Kottelat, 2013b).Despite this high diversity and theirimportance for humans, our knowledgeof fish biology over most of Asia is stillvery incomplete and often is restrictedto mere lists (Kottelat & Whitten, 1996).Large areas are still unsurveyed.

In a review of the conservation sta-tus of fish in mainland Southeast Asia,Kottelat et al. (2012a) reviewed themajor threats affecting freshwaterfishes. They found that alteration of rivermorphology is the single most importantthreat since it modifies or suppressesthe habitats and the hydrological fea-tures upon which the fish depend.Among these alterations, the develop-ment of dams and reservoirs is the mostcrucial threat.

A number of the impacts are intrinsicto the creation of reservoirs, like the

suppression of a part of the habitats inthe reservoir and downstream of a damor downstream of a diversion channel,or the interruption of migratory road,and must be addressed and mitigated atthe conception of the project. In areaswhose fish fauna is still superficiallyknown (as is the case in most of Laos),extensive surveys and collection ofbaseline data is an absolute necessity.The surveys should not be restricted tothe directly impacted area but mustinclude adjacent areas, in as well asoutside the impacted river system.

The information on Laotian fishespublished in the scientific literature isstill very limited. Proper scientific sur-veys of the fish diversity started in themid-1990s in conjunction with hydro-power development. Without underes-timating the environmental impacts ofthe project, surveys conducted in theframework of the Nam Theun 2 projectare unique in Laos for various extents:(i) the baseline studies that have been

The fishes of the Nam Theun and Xe Bangfai drainages, Laos 3

conducted before construction, (ii) thequantity of information that have beenassembled, made publicly accessibleand that have been used for scientificresearch.

This essay briefly presents theresearches that have been conductedbetween 1996 and 2012, the fish faunaof the Nam Theun and Xe Bangfaidrainages and the status of the speciesof special concern.

2 METHODS AND TERMINOLOGY

Over the years, fish samples wereobtained with almost all possible meth-ods: electricity, gill nets, castnets,seines, pushnets, kicknets, hook andline, traps, spears, and ichthyocides.Explosives were never used althoughfishes killed by poachers have occa-sionally been observed. All possibleexisting habitats have been surveyed,including headwaters, riffles, runs,deep pools, main rivers, waterfalls, rap-ids, swamps, lakes and caves. Sam-pling sites of very difficult accesses, upin the Annamite range or in the gorgeswere reached by helicopter. Surveyswere conducted in 1996, 2002, 2003,2006, 2007, 2009, 2011 and 2012.Samples were obtained at 243 sites;most sites were sampled once, butsome were sampled by up to 5 surveys.

Species are recorded only undertheir scientific names (see Kottelat,2013b for the latest update of thenomenclature of the fishes of freshwa-ters in Southeast Asia). The term "sp."means an unidentified species. Theterm "aff." means that a population can-not be identified with any known speciesbut is close to a named species (for

example Microcobitis aff. misgurnoidesis distinct but close to Microcobitis mis-gurnoides. The term “cf." indicates thatthe population is likely to belong to thespecies referred to but the identificationis not yet certain because of unresolvedtaxonomic problems.

In the discussion, endemic is usedas either a noun or an adjective means:whose distribution is restricted to a geo-graphically limited area. For example, aspecies endemic to the Nam Theun isa species that has been observed onlyin the Nam Theun drainage.

Spelling of names of villages, moun-tains, and streams follow either theNTPC standard toponymy or the 19851:100,000 Lao P.D.R. topographicmaps. Coordinates were obtained frommaps in the early years and with a vari-ety of GPS after 2000. Datum: WGS 84,UTM zone 48.

Limitations. Ideally, we should beable to select more or less random sitesfor survey. This is rarely feasible for dif-ferent reasons, among which: (i) theplaces were the river is accessible byland may not be suitable for sampling;(ii) it may be impossible to land by boatat a given site; (iii) the presence of a vil-lage or a fishing camp does not allowthe use of some methods; (iv) or theavailable equipment does not allowgood sampling of large rivers or deepwaters, or very fast current. These lim-itations are most obvious for the work inthe lower Nam Theun (downstream ofthe Nakai Dam), several stretches ofwhich can only be accessed by helicop-ter (as done in 1996, 2006 and 2007) orby long walks along dangerous shores,which is not possible with heavy equip-ment. The number of places allowing asafe access to the river is limited, and

4 M. Kottelat

then one needs to be able to safelymove around, to find a spot where it ispossible to set (and recover) nets, toapply chemicals, to recover the sam-ples. Safety is a very important limita-tion because of the very strong current,slippery rocks, etc.

Conventions. Upper Nam Theunrefers to the Nam Theun Riverupstream of the Nakai Reservoir. LowerNam Theun refers to the Nam TheunRiver downstream of the Nakai Dam.

Keng Louang: in Laos, most rapidshave a proper name, and on many riv-ers there is one or more called KengLouang (literally "large rapids"). TheNam Theun has two Keng Louang, onefar downstream of the reservoir, theother at about FSL (Full Supply Level).The Nam Xot has one Keng Louang,below FSL.

NPA stands for National ProtectedArea, as used here it implies theNakai–Nam Theun NPA.

SL stands for standard length (thelength of a fish without the caudal fin);masl for meters above sea level.

3 FISH SURVEYS: CHRONOLOGYAND SIGNIFICANCE OF NAM THEUN2 PROJECT ON KNOWLEDGEOF LAOTIAN FISH FAUNA

The first mention of fishes of Laos inthe scientific literature dates back to1878 when Sauvage (1878, 1880)described a few fishes collected byJules Harmand (Kottelat, 1984).

Nothing else was published until the1930s, when some fishes were col-lected during ornithological expeditionsby J. Delacour (Hennache & Dickinson,2000; Kottelat, 2012c: 51) and described

by Pellegrin (1936) and Pellegrin &Fang (1940).

Sérène (1951) compiled a first list ofthe fishes of Laos and Taki (1974) pub-lished a book summarising the knownfauna and its distribution. However,the published scientific data on fishdistribution and biology were virtuallyrestricted to the Mekong mainstream(Kottelat, 1989; Roberts, 1993). Exceptfor limited data on the Nam Ngum 1Reservoir and isolated descriptions ofnew species there was no data on thefish fauna of the tributaries and head-waters.

A first survey of the fishes of theNam Theun and Xe Bangfai was verysuperficial, with about 54 speciesobserved, with numerous identificationproblems.

As of March 1996, about 210 fishspecies were known from Laos. Thefirst survey of the fishes of the NamTheun and Xe Bangfai yielded 165species (Kottelat, 1996), which is equalto 79% of what was known before forthe whole country. In fact 46 of thesespecies had not been recorded beforein the country. In one month the fishfauna of Laos had increased to 256species. Several of these 46 specieswere known from Thailand, Vietnam orChina, but 16 were apparently new toscience and ipso facto endemic to theNam Theun 2 project area.

The next year, surveys were con-ducted in order to try to find these 16endemics outside the project area(Kottelat, 1997). The Xe Banghiang(the drainage immediately South of theXe Bangfai) was surveyed. For safetyand logistics reason it was no possibleto survey the Nam Kading and NamXan immediately north of the Nam


Theun, and rivers were surveyed fur-ther North in Laos. These surveysobtained 233 fish species in 5 weeks,that is, about as many species thatwere already known in the country afterthe 1996 survey. The surveys added55 species to the fauna of Laos, ofwhich 35 were new to science. The sur-veys also discovered some of the puta-tive endemics in the Xe Banghiang andthey also allowed to show that most ofthe species endemic to the project areawere present upstream of the impactedarea.

In 1999 I was asked to compile thereports of the surveys conducted forNam Theun 2 and other projects into aguide to the fishes of Laos. This projectwas supported by a grant from WorldBank/Netherlands Partnership Pro-gram. In order to have a more completecoverage, several additional drainageswere surveyed. These surveys as wellas works of other researchers (e.g.Baird et al., 1999) brought the fishfauna of Laos to 481 species (Kottelat,2001). From 210 species in March1996 and to 481 in June 1999, the fishfauna of Laos had increased by 228%.These surveys allowed the discovery of128 species new to science (Kottelat,1998, 2000; Ng & Kottelat, 1998, 1999,2000a-c; Ng, 1999a-b; Chen et al.,1999; Kottelat & Bréhier, 1999; Fang &Kottelat, 1999, 2000; Britz & Kottelat,1999a-b; Kottelat & Ng, 1999; Chen &Kottelat, 2000).

Since, species continued to beadded by other surveys and otherresearchers and the total fish fauna ofLaos is now about 520.

After the 1996 survey of NamTheun 2 project area, Roberts (1998b,1999) described additional species he

had obtained on Nakai Plateau. The1999 survey also found more of the'endemic' species outside the NamTheun 2 project area and further taxo-nomic research revealed that some ofthe species identified in 1996 were infact a mixture of several species. In2002, two species remained (Scaphog-nathops theunensis, Tor ater) thatwere known only from the impactedarea and surveys were conducted in2002 and 2003 to try to find them out-side the impacted area and to obtaininformation on their biology and lifecycle (Kottelat, 2002, 2004).

With the start of the constructionphase of the Nam Theun 2 project, addi-tional surveys were conducted in 2006,2007, 2009 and 2012 to collect base-line data and for monitoring (Kottelat,2006, 2007, 2009, 2013a).

The surveys done in connection withthe Nam Theun 2 project contributeddirectly or indirectly to the documenta-tion of more than half of the fish faunaof Laos. Fish surveys have been con-ducted for other hydropower projects inthe country. Most are not publicly avail-able, or are not usable. Only very fewothersurveysproduceddata that resultedin scientific publications (Roberts, 1995,1997, 1998a; Baird et al., 1999).

4 THE STUDY AREA

The investigated area covers thedrainages of the Nam Theun and XeBangfai (Fig. 1). The Xe Bangfai is aneast-side tributary of the Mekong,entering it about 50 km south of Tha-khek. The Nam Theun is adjacent to theXe Bangfgai to the North; it joins theNam Gnouang to constitute the Nam

6 M. Kottelat

Fig. 1. Map of Nam Theun and Xe Bangfai drainages showing sites sampled by fish biodiversity sur-veys between 1996 and 2012.Fig. 1. Carte des bassins de la Nam Theun et la Xe Bangfai montrant les sites échantillonnés par lesinventaires ichtyologiques entre 1996 et 2012.


Kading, another large east-side tribu-tary of the Mekong, entering it south ofPaksan. Although adjacent, the two riv-ers have different topography, which isreflected by different fish fauna.

4.1 Nam Theun

The Nam Theun and its tributaries(the main ones are Nam On, Nam Noy,Nam Mon, Nam Xot and Nam Nian)originate on the Laos-Vietnam bound-ary, 1000-2200 masl, and flow perpen-dicular to it, northeast-southwest. Theserivers have a high gradient and areinterrupted by many large rapids andwaterfalls. Their bed is mainly made oflarge blocks, boulders and stones,except for a threshold of a few km atabout 560 masl with relatively slowwater, with sandy bottom and shores.From there, the Nam Theun and its trib-utaries descend to Nakai Plateauthrough deep and steep gorges, in asuccession of rapids (now flooded, atleast part of the year).

The Nam Theun and its tributariesflow parallel to each other until theyreach Nakai Plateau. Although the pla-teau is quite flat (altitude about 530 masl)and has only a very shallow ridge abovea steep slope directed northeast-south-west, the Nam Theun makes a sharpright angle turn northwest and is joinedby its tributaries.

The Nam Theun meanders on theplateau in a succession of relativelyslow runs, shallow rapids and deeppools. The substrate varies from sand(especially at mouth of tributaries, e.g.Nam Xot, Nam On) to rocks. The waterwas usually clear in the dry season.

An extensive area of the plateau wasnaturally flooded in the wet season, but

in the dry season only mud pools and afew deeper lakes subsisted.

The Nam Theun leaves the NakaiPlateau through long and narrowgorges. In this stretch, until 2008, theNam Theun was a succession of rapidsand a waterfall (that disappeared in therainy season). Along this stretch theNam Theun receives a single tributary(Nam Phao), which also originates onthe Laos-Vietnam border and alsoflows parallel to the other Nam Theuntributaries. The Nam Theun has no sig-nificant tributaries on the left side.

About 70 km after leaving the NakaiPlateau, the Nam Theun joins the NamGnouang (another river descendingfrom the Laos-Vietnam divide) and theybecome the Nam Kading. The NamKading enters again gorges for about70 km to reach the lowland, and thenthe Mekong. Shortly downstream of theconfluence of the Nam Theun and NamGnouang, a dam created the Theun-Hinboun Reservoir and diverts part ofthe waters of the Nam Kading to theNam Hinboun, another tributary of theMekong; an extension dam on the NamGnouang stocks more water for theTheun-Hinboun Reservoir.

4.2 Xe Bangfai

The Xe Bangfai topography is verydifferent from that of the Nam Theun.

The sources of the Xe Bangfai arelocated along the Laos-Vietnam bound-ary at about 17°N 106°30'E. The alti-tude of that area is around 700 masl. Itfirst flows southeast-northwest, in aquite narrow valley and through twodeeply dissected limestone areas. Ithas a typical morphology of highland

8 M. Kottelat

river, with a bed made of stones andboulders. It has nowhere a strong gra-dient and no large rapids or waterfallcould be seen from the air. After about70 km it disappears in a natural tunnel.The distance between the entrance ofthe tunnel and the resurgence is about5 km at the surface. The tunnel is knownto foreigners since Cupet (1900: 191,map 8). Contrary to some other naturaltunnels in the Khammouane karst it hasnumerous waterfalls and cannot betravelled by boat or used as passagebetween two valleys. Nevertheless, ithas been crossed as early as 1905(Macey, 1908, 1911) and since it hasbeen mapped and explored (Mouretet al., 1996, 1997a-b, 2010; Pollack &Osburn, 2006; Pollack et al., 2009).

From the resurgence, the Xe Bang-fai flows west until about Mahaxai,across a plain with several massives oftower karst. On this plain, before reach-ing the area of the Nam Theun 2project, the Xe Bangfai was a large, rel-atively shallow and slow flowing river,interrupted only by a few shallow rap-ids. In 1996 the water was clear as faras downstream of Mahaxai; this was nolonger the case in 2006, with increasedhuman activity. Downstream of Mahaxai,the Xe Bangfai turns southwards andenters a hill range where it goesthrough various rapids, none of signifi-cant size, and at least one very deeppool. After the gorges, it enters theMekong floodplain and the Mekongitself.

The Xe Bangfai has two main tribu-taries, the Xe Noy and Nam Oula, whichare shallow slow flowing streams. Onmost of its course, the Xe Bangfai flowsin karstic formations, which explainsthat it has very few surface tributaries,

and that most of them are temporary orhave water only in their lowermostcourse. Also, because of the karstic for-mations and the absence of surfacewater, most of the middle and lower XeBangfai drainage is characterised bylarge quantities of sand and dust in thedry season, a phenomenon alreadyreported in the first published descrip-tion of the area (Cupet, 1900: 185).

The karst massive is very extensiveand is shared with the Xe Done andNam Hinboun drainages and alsoextends to Vietnam. Beside the XeBangfai tunnel already mentioned, sev-eral streams have underground courses.Numerous caves have already beenexplored and a number of troglobyteanimals have been discovered, includ-ing three species of fishes (Kottelat &Bréhier, 1999; Kottelat & Steiner, 2011;Vidthayanon & Jarutanin, 2002).

5 FISH FAUNA

The species now known to occur inthe Nam Theun and Xe Bangfai drain-ages and their distribution outside thesedrainages are given in Appendix 1.

5.1 Nam Theun drainage

Seventy-four fish species havebeen recorded in the Nam Theun andNam Gnouang drainages. The two riv-ers join to form the Nam Kading. Thefish fauna of the Nam Gnouang is stillincompletely surveyed but for what isknown, in the lowermost section, it isidentical to that of the Nam Theun(from data of the 1996 and 2002 sur-veys). The fauna of the upper part of


the Nam Gnouang drainage, however,could differ from that of the NamTheun. More surveys may have beenconducted for other projects but thedata have not been made public. Thelist of the native species recorded inthe Nam Theun is presented in Table I.

The fauna of the Nam Theun ispeculiar by its high proportion ofendemic species, 21 out of 74 (28%).Noteworthy, a number of these endem-ics belong to genera known from theeastern slope of the Annamitic range,in Vietnam and in southern China (e.g.Rhodeus laoensis, Microcobitis aff.misgurnoides), which is a distinctzoogeographic unit. Other species arenot known from elsewhere in theMekong drainage but are widely dis-tributed in Vietnam and South China(e.g. Hemibarbus cf. umbrifer). Pres-ently there is no hypothesis explainingthis distribution pattern.

Another example of an East Asianspecies present in the Nam Theundrainage is Misgurnus anguillicaudatuspresently known only from near BanNape (on Nam Phao upstream of LakSao). This species inhabits swampsand rice paddies and can be trans-ported out of water for a long period andit could have been transported byhumans across the divide. If the speciesis not native, the introduction must havehappened at least 50 years ago sinceolder persons interviewed in villagescommented that the species hasalways been present. The other 'Viet-namese' species are less likely to havebeen introduced by humans since theywould not survive the transport, they areof no special food interest, and theywere found only far up in the tributariesof the Nakai Reservoir, in the Nakai

NationalProtectedArea(NPA),upstreamof the last village.

The first survey in 1996 recorded 60species in the Nam Theun. The follow-ing surveys added 14 species. Eventhe 2012 still added 2 species. Thissuggests that additional surveys stillmight add a few species. The numberof potential additional species in theupper Nam Theun is probably very low.This is not the case for the lowermoststretch. The two additional speciesrecorded by the 2012 survey wereobtained in the lower Nam Theun(Ambastaia nigrolineata, Puntioplitesfalcifer). It is not clear whether theincrease of the number of species inthe lower Nam Theun is due to a lessintensive sampling because of themore difficult (and expensive) access,or if it is the result of species from theslow flowing waters from near theTheun–Hinboun Reservoir now beingable to move upstream because of thevery much reduced flow (e.g., Param-bassis sp. 'slender'). Exotic specieshave also appeared in the reservoirand some have the potential to becomeinvasive (e.g. Parambassis siamensis,Cottet et al., same issue).

Although most of the species origi-nally recorded on Nakai Plateau havedisappeared after inundation, all havebeen observed since, upstream ordownstream of the reservoir. The singleexception is Pangio aff. fusca, which isnot conclusive since the species hadbeen collected only in 1996 in crevices,an habitat difficult to sample. The latersurveys, before and after constructionof the dam did not obtain that species.

Whether all the species endemic tothe Nam Theun drainage will be ableto maintain over time is still an open

10 M. Kottelat

Table I. Native fish species recorded in the Nam Theun drainage, their general distribution outside NamTheun, the level of knowledge of their biology, and their biodiversity importance. Biology: 0 = unknown;1 = partly known; 2 = known. Distribution: a = widely distributed in Southeast Asia; b = widely distributedin Mekong drainage; c = widely distributed and/or abundant upstream of the inundation zone or in othertributaries of the Nam Theun; d = range totally or largely in inundation zone and/or in Nam Theun down-stream.Tableau I. Poissons indigènes recensés dans le bassin de la Nam Theun, leur distribution générale endehors du bassin de la Nam Theun, le degré de connaissance de leur biologie et leur importance entermes de biodiversité. Biologie : 0 = inconnue ; 1 = partiellement connue ; 2 = connue. Distribution :a = espèce largement distribuée en Asie du Sud-Est ; b = espèce largement distribuée dans le bassindu Mékong ; c = espèce largement distribuée et/ou abondante en amont de la zone d’inondation oudans d’autres affluents de la Nam Theun ; d = espèce totalement ou en partie présente dans la zoned’inondation et/ou dans la Nam Theun en aval.

BiologyBiodiversity

importance in contextof present report

Distribution General distribution(raw outline)

importantless

importanta b c d

Anguillidae

Anguilla marmorata (?) 1 x x Indo-West Pacific;occasional in Mekong

Cyprinidae

Amblypharyngodonchulabornae

1 x x Mainland Southeast Asia

Bangana elegans 0 x x Nam Theun - NamGnouang endemic

Barbodes aurotaeniatus 0 x x Mekong drainage

Cyclocheilichthys armatus 1 x x Southeast Asia

Cyclocheilichthys repasson 1 x x Southeast Asia

Devario fangfangae 0 x x Nam Theun - NamGnouang endemic

Esomus metallicus 1 x x Mainland Southeast Asia

Folifer cf. brevifilis 0 x x Southeast and East Asia

Garra cambodgiensis 0 x x Mainland Southeast Asia

Garra cyrano 0 x x Middle Mekong drainage

Garra theunensis 0 x x Middle Mekong drainage

Hampala macrolepidota 1 x x Southeast Asia

Hemibarbus cf. umbrifer 0 x x East Asia

Hemiculterella macrolepis 0 x x Middle Mekong drainage

Hypsibarbus vernayi 1 x x Mainland Southeast Asia

Luciocyprinus striolatus 0 x x Middle Mekong drainage

Mystacoleucus marginatus 1 x x Southeast Asia

Neolissochilus blanci 0 x x Mekong dbasin

Onychostoma fusiforme 0 x x Middle Mekong drainage

Poropuntius carinatus 0 x x Middle Mekong andSalween drainages

Puntioplites falcifer 1 x x Mekong drainage

Puntius brevis 0 x x Southeast Asia


Table I. Continued.Tableau I. Suite.

BiologyBiodiversity



importantless

importanta b c d

Raiamas guttatus 0 x x Southeast Asia

Rasbora paviana 0 x x Mainland Southeast Asia

Rhodeus laoensis 0 x x Nam Theun endemic

Scaphiodonichthysacanthopterus

0 x x Mekong and Chao Phrayadrainages

Scaphognathops theunensis 0 x x Nam Theun - NamGnouang endemic

Tor ater 0 x x Nam Theun endemic

Tor laterivittatus 0 x x Middle Mekong drainage

Tor tambra 0 x x Southeast Asia

Tor tambroides 0 x x Southeast Asia

Gyrinocheilidae

Gyrinocheilus aymonieri 1 x x Mainland Southeast Asia

Balitoridae

Balitora lancangjiangensis 0 x x Middle Mekong drainage

Balitoropsis yunnanensis 0 x x Mekong basin

Hemimyzon papilio 0 x x Middle Mekong drainage

Homalopteroides smithi 0 x x Mainland Southeast Asia

Nemacheilidae

Nemacheilus arenicolus 0 x x Nam Theun endemic

Schistura atra 0 x x Nam Theun endemic

Schistura cataracta 0 x x Nam Theun endemic

Schistura dorsizona 0 x x Middle Mekong drainage

Schistura kongphengi 0 x x Middle Mekong drainage

Schistura nudidorsum 0 x x Nam Theun endemic

Schistura obeini 0 x x Nam Theun endemic

Schistura sombooni 0 x x Middle Mekong drainage

Schistura tubulinaris 0 x x Nam Theun endemic

Cobitidae

Lepidocephalichthys hasselti 0 x x Southeast Asia

Microcobitis aff.misgurnoides

0 x x Nam Theun-NamGnouang endemic

Misgurnus anguillicaudatus 2 x x East Asia

Pangio aff. fusca 0 x x Nam Theun endemic

Botiidae

Ambastaia nigrolineata 0 x x Mekong and Chao Phrayabasins

Bagridae

Hemibagrus wyckioides 1 x x Mekong drainage

Pseudomystus siamensis 0 x x Mainland Southeast Asia

12 M. Kottelat

Table I. Continued.Tableau I. Suite.

BiologyBiodiversity



importantless

importanta b c d

Siluridae

Pterocryptis inusitata 0 x x Nam Theun endemic

Clariidae

Clarias cf. batrachus 3 x x Southeast Asia

Sisoridae

Bagarius yarrelli 1 x x Southeast and South Asia

Glyptothorax horai 0 x x Middle Mekong drainage

Glyptothorax laosensis 0 x x Mekong and Chao Phrayadrainages

Glyptothorax aff. zanaensis 0 x x Middle Mekong drainages

Oreoglanis hypsiurus 0 x x Nam Theun endemic

Oreoglanis lepturus 0 x x Nam Theun endemic

Pseudechenei sympelvica 0 x x Mekong basin

Adrianichthyidae

Oryzias pectoralis 0 x x Nam Theun endemic

Oryzias sp. 'river' 0 x x Nam Theun endemic

Oryzias sp. 'swamp' 1 x x Nam Theun endemic

Synbranchidae

Monopterus javanensis 2 x x Southeast and East Asia

Ambassidae

Parambassis sp. 'slender' 0 x ? x Nam Theun endemic ?

Odontobutidae

Neodontobutis aurarmus 0 x x Mekong basin

Gobiidae

Papuligobius ocellatus 0 x x Mekong basin

Rhinogobius lineatus 0 x x Nam Theun endemic

Anabantidae

Anabas testudineus 2 x x Southeast and South Asia

Osphronemidae

Trichopsis schalleri 1 ? x Mekong basin

Channidae

Channa gachua 1 x x Southeast Asia

Channa striata 2 x x Southeast and South Asia

Mastacembelidae

Mastacembelus armatus 0 x x Southeast and South Asia


question. Most concerned species areScaphognathops theunensis, Oryziassp. 'swamp', and Rhodeus laoensis.Luciocyprinus striolatus, a rare and glo-bally endangered species, is also ofspecial concern.

5.2 Xe Bangfai drainage

178 species have been recorded inthe Xe Bangfai drainage (Appendix 1).The fauna of the Xe Bangfai is similarto that reported for the other main trib-utaries of the Mekong in Laos, from the

Table II. Fish species endemic to the Xe Bangfarange totally or mainly in NTPC area; b = range excTableau II. Espèces de poissons endémiques autermes de biodiversité. a = espèce totalement oub = espèce présente exclusivement ou principalem

Biodiversityimportance i

context of presreport

importantles

impo

Cyprinidae

Bangana musaei * x

Devario sp. 'green' x

Devario cf. quangbinhensis ?

Nemacheilidae

Schistura punctifasciata x

Schistura sp. 'Nam Kathang' x

Cobitidae

Acantopsis sp. 'dwarf males' ? x

Acantopsis sp. 'vertical spots' ? x

Sisoridae

Glyptothorax aff. fuscus 2 x

Odontobutidae

Terateleotris aspro x

* Bangana musaei is a biodiversity very important ssystem of the underground course of the Xe BangfNTPC activities.

Xe Kong in the South until the NamNgum in the North, at least in the flood-plain. Those of these rivers that havebeen studied tend to have distinctivefauna in the upper stretches. A singlesite could be efficiently sampled inthe upper stretch of the Xe Bangfai(upstream of its underground course).Only 9 species are apparently endemicto the Xe Bangfai (Tab. II). Only one ofthe species very similar to or possiblyshared with Vietnam (Devario aff.quangbinhensis) is of biodiversity impor-tance (small distribution range).

i drainage and their biodiversity importance. a =lusively or mainly upstream of NTPC activities.bassin de la Xe Bangfai et leur importance en

principalement présente dans la zone de NTPC ;ent en amont des activités de NTPC.

nent Distribution

srtant

a b

x cave species found in XeBangfai tunnel

x Nam Kathang Gnai

x ? x Nam Oula

x

x Nam Kathang Gnai

? x Lower Xe Bangfai

? x Nam Oula

x Xe Noy

x Upper Xe Bangfai

pecies with an extremely small range in the caveai. It is however totally outside the impact zone of

14 M. Kottelat

The Xe Bangfai drainage has a typ-ical Mekong floodplain fish fauna. Anumber of these Mekong species havenot yet been recorded in the Xe Bangfaibut are expected to be present. The2012 survey included habitats that hadnot been sampled before (because theywere not directly impacted by the NamTheun 2 operations). Four days of sam-pling (7 sites) yielded 29 additional spe-cies. Most were from tributaries andswamps. Four of these additional spe-cies are presently known only from theXe Bangfai; some will certainly be dis-covered in adjacent drainages but oth-ers are potentially endemic and biodi-versity important (Tab. II). Five of the XeBangfai endemics have their knownrange entirely or partly upstream of thearea directly impacted by Nam Theun 2activities.

5.3 Cave fishes

The Xe Bangfai crosses severalextensive karst massives. Several fishspecies have been observed in caves.These are mostly individuals of surfacespecies showing no sign of adaptationto underground life. The exception isBangana musaei that has been observedonly in caves around the upstreamentrance of the underground stretch ofthe Xe Bangfai, far upstream of the areaimpacted by Nam Theun 2 activities(Kottelat & Steiner, 2011). Another cavefish (Troglocyclocheilus khammouan-ensis) is known from the resurgence ofthe Nam Done from the karst massivebetween the Nam Done (a tributary ofthe Mekong) and Xe Bangfai drainages(on the road between Thakek andMahaxai) (Kottelat & Bréhier, 1999).Although the outlet is in the Nam Done

catchment, considering the morphologyand functioning of karst systems, theactual range of the species may extendfor a long distance and the speciescould potentially be impacted by theproject, especially by surface pollutionand lowering of the water table.

6 BIODIVERSITY IMPORTANTSPECIES

6.1 Rationale for focusing onbiodiversity important species

In the context of the impact of aproject on aquatic biodiversity, somespecies have a greater biodiversityimportance than others, either because:- their range is totally or largely impactedby the project; or a part of their rangevital at a period of their life-history cycleis totally or largely impacted by theproject (for example an obligatory andunique breeding site);- although they may have a large rangethey are rare throughout this range,their populations are declining quickly(or under a threat of sharp decline), orthey are protected or listed as endan-gered by local, national or internationallegal instruments (species that cannotbe fished; species whose trade is for-bidden or limited [e.g. CITES], etc.);- they have special evolutionary, scien-tific, emotional, or cultural importance(e.g. freshwater dolphin, giant Mekongcatfish).

6.2 Biodiversity important speciesin Nam Theun 2 project area

Most of the endemic species foundin the Nam Theun 2 project area have


narrow ecological requirements. Mostof them are specialised for habitats infast water and they are found exclu-sively in these habitats. On Nakai Pla-teau, before inundation, most of thesefast-water species were restricted toformer rapids or were present only at afew specific sites. In the inundatedzone, the species requiring rapids andfast water are now absent or have pop-ulations with fewer individuals. As theirrange upstream of the reservoir is notinundated, a part of their habitat remainsand is protected by the NPA. Inrepeated interviews in 1996, 2001,2003 and 2007, villagers constantlyanswered that no species was known tobe migrating or to have earlier migratedbetween the plateau and the upstreamNam Theun and Nam Xot or to use theplateau as exclusive spawning andnursery ground. However, they becomeindirectly impacted, for example byincreasing human population or humanactivity in the NPA (e.g. the introductionof exotics and their pathogens).

The species impacted by the inun-dation only in part of their range andwith strong populations upstream ofthe reservoir are classified as of lesserbiodiversity importance and do notseem of priority concern (Tab. I).

Some species endemic to the NamTheun, Nam Gnouang and Xe Bangfaidrainages occur in habitats or areaswhere their survival does not seem tobe an issue after impoundment (sug-gested by post-inundation surveys).These species are mainly small benthicfishes. They are Schistura atra, Schisturaobeini, Schistura tubulinaris, Schisturacataracta, Schistura nudidorsum,Nemacheilus arenicolus, Pterocryptisinusitata and Oreoglanis hypsiurus.

The survival of some midwater speciesis also considered not to be an issuesuch as Devario fangfangae, Param-bassis sp. ‘slender’ (suspected newspecies) and Oryzias pectoralis.

The present paper focuses on biodi-versity important species.

6.2.1 Oryzias sp. 'swamp'

Oryzias sp. 'swamp' (Fig. 2) is notyet named following the rules of theInternational Code of Zoological Nomen-clature and the name Oryzias sp.'swamp' is used awaiting the publicationof the formal description and the 'official'name. It is known only from the NakaiPlateau and its known distributionrange is almost totally inundated byNakai Reservoir.

The species was present in the sam-ples collected as early as 1996 but wasnot recognised. It was mixed withOryzias sp. 'river', which then was mis-identified as Oryzias sinensis. Oryziassp. 'swamp' is distinguished from

Fig. 2. Oryzias sp. 'swamp’, male (above) andfemale (below); about 15 mm SL (photograph ©by Hiromichi Nemoto).Fig. 2. Oryzias sp. 'swamp’, mâle (haut) etfemelle (bas) ; environ 15 mm LS (photographie© par Hiromichi Nemoto).

16 M. Kottelat

Oryzias sp. 'river' by morphologicalcharacters (especially in head shape,pigments on the head, maximum size,number of anal-fin rays). Molecular dataunambiguously show that it is distinctfrom Oryzias sp. 'river' and that both aredistinct from all known Oryzias species.

Oryzias sp. 'swamp' is the smallestfish (and vertebrate) species known onthe plateau. The largest size observedis 20 mm SL although most specimensare below 18 mm SL.

Before inundation, Oryzias sp.'swamp' was observed in the dry sea-son in most pools, ponds and swampson the Nakai Plateau (Kottelat, 2007),where it was often present in largenumbers. It survives the dry season inshallow pools, with high temperature,low or no dissolved oxygen, and highorganic pollution as these pools areusually used by water buffaloes. Thefish lives immediately under the watersurface, and its upturned mouth allowsit to breath in the very thin upper layerof water in contact with air.

However, these extreme habitatswere erroneously interpreted as spe-cialised habitat of the species. In factthe sites where it was most abundanthad cooler water, with submerged veg-etation. In these habitats, the males are'colourful' with conspicuous red bandsalong the lower and upper edges of thecaudal fin. These sexually dimorphiccolour marks are totally indistinct inmurky water.

Little is known on the biology of thespecies. Some aquarium observationsindicate that individuals of about 12-16 mm SL spawn 1 or 2 eggs per dayduring the warm-wet season (June–September 2012). It seems that in earlySeptember, the oldest individuals of

the offsprings had already started tospawn, which corresponds to about 3months. At hatching, the fry is about 4mm, which is smaller than known in allother species of the genus (K. Kubota,pers. comm., 2012). Finally, theseobservations suggest that Oryzias sp.'swamp' deposits the eggs on the sub-strate or in crevices while in the otherspecies of Oryzias the female carries acluster of eggs for a few days hangingnear the genital opening.

Search for Oryzias sp. 'swamp' in2009 and 2011 along the shores of theNakai Reservoir and in adjacent swampsand wetlands failed to find the speciesand it became of serious concern. Thespecies was 'rediscovered' in 2012 at asingle site. Investigations were con-ducted in the dry season 2013 by theWater Quality and Biodiversity depart-ment of the Nam Theun 2 Power Com-pany along the shores of the reservoir.This survey included 68 swamps andrecorded the presence of Oryzias sp.'swamp' at 8 sites. Most of the swampswhere the species was observed arelocated below full supply level of the res-ervoir (NTPC unpublished data; M.Cottet, pers. comm., 2014).

6.2.2 Oryzias sp. 'river'

Oryzias sp. 'river' (Fig. 3) too is notyet formally named and is temporarilycalled Oryzias sp. 'river'. It is knownonly from the Nakai Plateau and itswhole known distribution range is inun-dated by Nakai Reservoir. It was mis-identified as Oryzias sinensis in theearlier surveys. Before inundation, atthe end of the dry season the specieswas collected only in the Nam TheunRiver, in low numbers, in backwaters or


among shore vegetation. It seems thatwith the onset of the rainy season thisspecies moved to the flooded areaswhere it spawned. Other Oryzias spe-cies of similar size reach sexual matu-rity in about 10-12 weeks, and severalgenerations may succeed in a singleannual cycle as observed in its relativeOryzias sp. 'swamp'. When the waterlevel decreases it survives in pools andin the river. However, it seems thatmost individuals do not survive in poolswhen the water level becomes too low,possibly because of high temperatureand low water quality.

In 2012, the species was present inabundance all around the reservoir andin backwaters and immediately belowof the Nakai Dam. The species hasapparently adapted very well to reser-voir conditions and does not requireany management measure.

6.2.3 Scaphognathops theunensis

Scaphognathops theunensis (Fig. 4)is endemic to the Nam Theun and NamGnouang main rivers. In the Nam Theunits range is totally included in the areaimpacted by the Nam Theun 2 project.In 2002 a survey was conducted in theNam Gnouang to check its presence,distribution and habitat preferences(Kottelat, 2002). Since, the known dis-tribution in the Nam Gnouang is totallyincluded in the area impacted by the

Fig. 3. Oryzias sp. 'river’, adult female.Fig. 3. Oryzias sp. 'river’, femelle adulte.

Theun-Hinboun Reservoir and itsextension reservoir. Information gath-ered in 2007 and 2009 indicated that thespecies is present in the lowermostNam Phao, a tributary of the NamTheun River entering it downstream ofthe Nakai Dam. Scaphognathops th-eunensis could not be found down-stream of the confluence of the NamTheun and Nam Gnouang (down-stream known as Nam Kading).Research conducted in 2002 showedthat it is replaced by Scaphognathopsbandanensis in the Nam Mouang, a trib-utary of the Nam Kading.

The species lives in deep pools,usually immediately below riffles andrapids. Small juveniles had been col-lected in fast water at the future NakaiDam site in 1996. Apparently it feedsby scrapping algae growing on stonesand logs, and the micro-invertebratesliving among the algae, with the narrowlower jaw terminated by a cornifiedsheath.

Because of its habitat requirementsand feeding habits, it was expected thatScaphognathops theunensis would notsurvive in both the reservoir condition(Nakai Reservoir and Nam Gnouang

Fig. 4. Scaphognathops theunensis, adult,160 mm SL, collected in 1996 in Ban Thalang.Fig. 4. Scaphognathops theunensis, adulte,160 mm LS, collecté en 1996 à Ban Thalang.

18 M. Kottelat

Reservoir) and in the lower Nam Theunbecause of low post-inundation flow.With the 2002 survey’s condition, it wasconsidered that it would survive only inthe Nam Gnouang, if that river remainedecologically and hydrologically intact.Since that time, with the construction ofthe Theun-Hinboun extension on theNam Gnouang, the survival chances ofScaphognathops theunensis are verylow in this area as well.

The presence of the species in thelower Nam Phao was suggested byinterviews with local villagers in 2007and 2009. With the poor habitat qualityin the Nam Phao downstream of Lak-sao and the very poor condition of itstributary Nam Kata (i.e. low flow, warmwater, eutrophication, and severe localmining pollution), a potential populationin the Nam Phao cannot be consideredsafe and requires management meas-ures to ensure its survival.

In 2012, three individuals, about100 mm SL, were observed in thecatch of fishermen in the Nam Theundownstream area. This observationconfirmed the presence of the speciesand their size suggests that these indi-vuals were about 2-3 years old, whichimplies that they were born in 2009-2010, that is after completion of NakaiDam. This leads to suggest that thespecies had been able to survive (atleast temporarily) the low flow condi-tions. However, the parents were bornprobably 3-4 years before, which wasbefore completion of Nakai Dam.Future will show whether the individu-als born after closure of the dam will beable to reach maturity and spawn.

Villagers in the Nam Theun down-stream of the Nakai dam reported thatthe species was present in the lower

Nam Phao but not abundant, and wasalso present in the Nam Theun upstreamof the confluence with the Nam Phao.They considered the species now as'not common'. Finally, individuals’ sizewas reported to be smaller than beforeconstruction of Nakai Dam.

6.2.4 Luciocyprinus striolatus

Luciocyprinus striolatus (Fig. 5) isknown from the Nam Theun and NamGnouang drainages. Other populationsare known in the upper Xe Kong, NamNgiep and Nam Ou in Laos, and inXishuangbanna in Yunnan (China). In allthese areas it is rarely observed and theonly rivers where it has been regularlyseen are the Nam Gnouang and upperNam Theun. It is not present in theMekong main river or in the lower partsof its main tributaries. As most of theupper parts of the other main tributariesof the Mekong in Laos have not yet beensurveyed (or the results have not beenmade public), its presence in someadditional drainages cannot be excluded.In any case its range is very fragmented.

Fig. 5. Luciocyprinus striolatus; juvenile, 61 mmSL (above) and subadult about 400 mm SL(below).Fig. 5. Luciocyprinus striolatus ; juvénile, 61 mmLS (haut) et subadulte, environ 400 mm LS(bas).


Also, it cannot yet be excluded thatsome of these isolated populations infact are different species.

Luciocyprinus striolatus inhabitslarge deep pools. Its habitat on theNakai Plateau has been lost by inunda-tion and it is unlikely to maintain a sig-nificant population in the Nam Theundownstream of Nakai Dam. Its onlyknown intact habitats are the smallstretches of the Nam Xot and upperNam Theun. If the species does notmigrate and does not need to travellong distance to feed, it will apparentlysurvive in the deep pools above FSL.

Because it is a very large fish (up toat least 1.5 m, with villagers mentioningsizes above 2 m), the number of indi-viduals is predictably very low andoverfishing is an immediate threat. It ismost likely already overfished, even ifnot the object of a specific fishing activ-ity. In recent years, it also attractedattention as a target for sport fishing.Villagers from both above the reservoirand downstream of Nakai Dam inter-viewed during the surveys 1996, 2001and 2003 surveys all commented thatthe species is not migratory andspawns in January-February in rapids(Kottelat, 1996, 2002).

In 2012, L. striolatus was observedin the Nam Theun both upstream anddownstream of the Nakai Reservoir. Itis not known in the Nam Phao. In theupstream Nam Theun, four individualsabout 50-60 mm SL were observed atthe uppermost extremity of a pool,immediately downstream of the rapids/riffles. Villagers reported that they areno longer observing large individualsand that those they now collect are notmore than 30 cm long. They consider

that overfishing is responsible for theabsence of larger individuals.

6.2.5 Tor ater

Tor ater (Fig. 6) is definitivelyrecorded only from the Nam Xot andNam Theun upstream of Nakai reser-voir. Although originally described(Roberts, 1999) on the basis of speci-mens obtained from villagers in BanThalang there is no indication of its ear-lier presence on Nakai Plateau. A sur-vey conducted in 2002 in the NamGnouang and Xe Bangfai drainages toinvestigate its possible presence out-side the Nam Theun drainage failed tofind it (Kottelat, 2002). Its distributionand biology in the Nam Theun drainagewas investigated in 2003 (Kottelat,2004). Villagers do not report havingseen the species on the plateau and asfar as known it completes it whole lifecycle upstream of the plateau, as sug-gested by the presence of individuals ofthree age classes.

Adult Tor ater seem to inhabit deeppools and to spawn in riffles.

Fig. 6. Tor ater; juvenile, 180 mm SL (above)and adult, 460 mm SL(below).Fig. 6. Tor ater ; juvénile, 180 mm LS (haut) etadulte, 460 mm LS (bas).

20 M. Kottelat

The smallest known individuals 104-140 mm SL had been obtained in asmall creek.

The species was not observed bythe 2012 survey and no informationwere obtained. The site where juve-niles had been obtained in 2003 wasvisited in 2012 but a small village hasbeen established and sampling wasnot possible at this exact site.

The only information available onthis species were obtained by the 2003survey (Kottelat, 2004) and are very lim-ited. Study is needed to determine itsdistribution, ecological requirements,reproductionpattern,andpopulationsize.

6.2.6 Devario sp. 'green'

This species (Fig. 7) had been col-lected only in the Nam Kathang Gnai, abranch of the Nam Kathang on NakaiPlateau during the 2007 and 2012 sur-veys. It is new to science and presentlyknown only from this stream. The spe-cies is not affected by the inundation ofthe reservoir since this stream flowsdirectly to the Xe Bangfai, not to theNam Theun. However, some resettledvillages are located on and across thedivide between the Nam Theun andNam Kathang Gnai, and other villagesare very close to the divide. Then, themain expected disturbance of its habi-tat may be related to the disturbance byvillages (e.g. agricultural activities).

Fig. 7. Devario sp. 'green', 47 mm SL.Fig. 7. Devario sp. 'green', 47 mm LS.

Species of the genus Devario oftenhave a large range and are frequentwithin their range. For example, Devariofangfangae, which is endemic to theNam Theun and Nam Gnouang drain-ages, is mainly a species of foreststreams, but it is also regularly seen inother habitats, and has also beenobserved in the reservoir. Other spe-cies, on the reverse, may have veryrestricted ranges. Devario sp. 'green'was collected in a forest stream habitat,with little water, and probably has thesame ecological requirements. It wasexpected that the species would bepresent elsewhere in the Nam Kathangor in the Xe Bangfai drainages. Thebaseline survey conducted in 1996 and2006 did not show its presence in the XeBangfai drainage, but the focus thenwas on the Xe Bangfai main river. Hab-itats similar to the upper Nam KathangGnai were not sampled at that timebecause none could be accessed.

Attempts to find Devario sp. 'green'outside the Nam Theun 2 project areafailed. The only other Devario speciesobserved in the Xe Bangfai drainageduring the surveys was in the NamOula catchment; it is a conspicuouslydistinct species, possibly new to sci-ence. Adjacent areas in Vietnam areinhabited by Devario quangbinhensis,a species somewhat similar to the NamOula one. Anyway, the endemism ofDevario sp. 'green' to Nam Theun 2project area should be confirmed bysearch for possible additional popula-tions outside the Nakai Plateau. Thepresence of a second species of thegenus in the Nam Oula suggests thatthe distribution of Devario sp. 'green'might not be very wide since there is noknown instance in Southeast Asia of


two species of Devario occurringtogether. Alternatively, this might sug-gest that the two species have differentecological niches.

If Devario sp. 'green' were to turnout to be restricted to Nakai Plateau,then management measures shouldinclude e.g. forest cover conservationalong the stream, prohibit waterabstraction to ensure a constant flow,even low, during the dry season.

6.2.7 Bangana elegans

Bangana elegans (Fig. 8) is pres-ently known only from the Nam Kadingdrainage (Nam Theun and NamGnouang Rivers). An earlier tentativerecord from Nam Ngum was based ona juvenile that could not be identifiedwith accuracy (Kottelat, 2001). AdultBangana recently collected in the NamNgum and Nam Ngiep have been iden-tified as Bangana lippa. There is nodata available for intermediate areas.The presence of a Bangana species isexpected in headwaters of most riversnorth of the Nam Gnouang. Banganaelegans could be present in the drain-ages immediately north of the NamGnouang, at least in the Nam Kadingdrainage. There is no record of Ban-gana species south of the Nam Theundrainage.

Fig. 8. Bangana elegans: juvenile, 133 mm SL.Fig. 8. Bangana elegans : juvénile, 133 mm LS.

Bangana elegans inhabits rapidsand fast flowing waters, and spawns atrapids. It disappeared from the NakaiPlateau after inundation of the reser-voir. It is expected to become rare ordisappear in the downstream NamTheun. It has been observed in theUpper Nam Theun, the Nam Xot, andNam Noy and individuals from about 2to 30 cm had been observed, in theearlier surveys, suggesting that it com-pletes it whole life cycle in thesestretches of the rivers. In 1996 villagersin Ban Thalang reported that Banganaelegans undertakes small local migra-tions to spawn in rapids in November,while people at Nakai Dam sitereported its presence year round. Itspawns on shallow rocks (reportedlyless than 10 cm deep). Spawning inshallow water means that the eggs andearly larvae would not survive adecrease of water level during the fewdays between spawning and the timethe larvae can move away. The timeneeded is not known but can beexpected to be 1-2 weeks. Further, vil-lagers used to catch this species withtrident in the rapids during spawning.With less water and shallower rapids,this fish becomes an easier target.Since impoundment of the Nakai Res-ervoir, the species has never beenseen in the inundation zone, except inthe parts of Nam Noy (M. Cottet, pers.comm., 2014), Nam Theun and NamXot, where these rivers are under FSL.

6.2.8 Rhodeus laoensis

Rhodeus laoensis (Fig. 9) is endemicto the Nam Theun and Nam Gnouangdrainages. In the Nam Theun, before

22 M. Kottelat

inundation it had been observed mainlyon the Nakai Plateau and in small trib-utaries of the Nam Theun upstream. Onthe plateau (inundation zone) it wasfound only in the main river and in foreststreams and has never been observedin the swamps. This species wasextremely frequent, and during the2001, 2006 and 2007 surveys verysmall juveniles were abundant. It pre-fers sections of forest streams with slowor standing water with submerged veg-etation and soft bottom, often close todeeper water. If the habitat becomesdisturbed by human activity and the cur-rent becomes slower and the waterslightly turbid, it replaces the typicalspecies of this habitat (especiallyDevario fangfangae and Rasbora pavi-ana), which become less abundant.This species was also observed down-stream of the Nakai Dam area in theNam Phao in 2007.

Fig. 9. Rhodeus laoensis; male, about 40 mmSL (above) and female, about 40 mm SL withblack ovipositor tube (below).Fig. 9. Rhodeus laoensis ; mâle, d’environ 40 mmLS (haut) et femelle, d’environ 40 mm LS avecun tube ovipositeur noir (bas).

Rhodeus laoensis is a bitterling, agroup of fishes that spawn their eggs inmussels, where they hatch and remainfor 1 to 8 months. The length of the stayin the mussel depends on the bitterlingspecies. There is no data for Rhodeuslaoensis but the small size of the free-swimming juveniles suggests it isamong the species spending only ashort time in the mussel. Bitterlings can-not complete their life cycle without themussel and their survival is thereforeabsolutely dependant of the presenceof the mussel. Each species of bitterlingneeds the presence of one (or a few)precise species of mussel (e.g. Liuet al., 2006; Kitamura, 2007), and if thatspecies is not present it will not useother species. While the fish may movefor some distance if habitat conditionsbecome unfavourable, the adult musselcannot move. If the stream bedbecomes exposed, polluted, silted oranoxic the mussel dies and this maylead to the local extirpation of the fish.

The mussel has a larval stage,called glochidia. The larvae are para-sitic and attach to the gills and fins offishes until they metamorphose, thenthey drop to the bottom. This meansthat the mussel has the potential to becarried by fishes in new habitats or tobe carried back to habitats from whichthey had been extirpated. As they needto be permanently in water, of coursethey would be unable to establish in thedrawdown zone. The time needed formetamorphosis varies depending onspecies, and there is no data for themussel of the Nam Theun drainage.Depending on the species, glochidiamay need one or a few precise fishspecies to attach, or may be more gen-eralistic and attach to many different


fish species. If the glochidia need toattach to a precise fish host (other thanthe bitterling), then the survival of boththe mussel and the bitterling depend ofthe survival of this host.

The mussel host Rhodeus laoensisis not yet objectively known, but a singlespecies has been collected in the NamTheun drainage. It belongs to the familyUnionidae, as all species used by bit-terlings. It has been identified as Pseu-dodon vondembuschianus (Fig. 10,identification by A. Bogan). The popu-lation from Laos had been identified byBrandt (1974) as a subspecies P. v.tumidus. The distribution of Pseudodonvondembuschianus includes mainlandSoutheast Asia, Sumatra, Java andBorneo. Some authors consider thatpopulations from the Mekong drainagein Laos and Cambodia are a speciesdistinct from those from Indonesia, butthis is still debated.

Fig. 10. Pseudodon vondembuschianus, theonly species of mussel observed in Nam Theundrainage, in which Rhodeus laoensis probablydeposits its eggs.Fig. 10. Pseudodon vondembuschianus, laseule espèce de moule observée dans le bas-sin de la Nam Theun, dans laquelle Rhodeuslaoensis dépose probablement ses œufs.

Rhodeus laoensis had not beenobserved in the inundation zone after2007. After the impoundment, specimenswere observed from villagers in theNam Theun downstream of the NakaiDam (M. Cottet, pers. comm., 2014). Ithas been observed in 2012 in the NamTheun upstream of the reservoir.

In the Nam Theun drainage, themussel Pseudodon vondembuschi-anus was observed in 2009 and 2012in the Nam Phiat, a small tributary ofthe Nam Phao. The presence of livemussels in a habitat should not betaken as meaning that the mussel issafe. Many species of Unionidae canlive very old (one species up to120 years) and some species still havesurviving individuals but they are func-tionally extinct because they only sub-sist as a few localised populationsmade only of old individuals no longerreproducing, or the number of individu-als is too low to support a viable popu-lation (Bogan, 1993). A bitterling depend-ing of a functionally extinct species ofmussel would be condemned to extinc-tion unless an alternative host can befound. A number of species of musselshave disappeared following the con-struction of dams in North America(Bogan, 1993, 2006; Watters, 2000).

Many species of bitterlings suc-cessfully breed in captivity (Akai et al.,2005) and the conservation program ofat least one species in Korea is basedon captive breeding. Captive breedinghas always been in presence of themussel.

Pseudodon vondembuschianus or avery similar species of mussel was col-lected in the Ban Done drainage, whereit was common. The identity of this sam-ple has not yet been confirmed. The

24 M. Kottelat

presence of a population of this speciesnear Nakai Plateau is important as itmight be a source of material usable forcaptive breeding of Rhodeus laoensisor for research. Other species of mus-sels were also collected in the XeBangfai drainage.

Because the presence of the mus-sel is necessary to allow the completelife cycle of Rhodeus laoensis, man-agement measures should focus onboth the fish and the mussel (Kottelat,2012b). It is necessary to confirm thatPseudodon vondembuschianus is thespecies used by Rhodeus laoensis andthat Rhodeus laoensis is the speciesused by the glochidia of this mussel.Should there be more than one speciesof mussel, there would be the risk oftargeting conservation measures at thewrong species. This requires eitherdirect observation of spawning orsearching for eggs or fish larvae in themussels. It is also necessary to estab-lish which fish species is/are used bythe glochidia (the larvae of the mussel).

6.2.9 Pangio aff. fusca

Pangio aff. fusca (Fig. 11) was ear-lier identified as Pangio fusca, a spe-cies then believed to be widely distrib-uted from the Salween to the Mekongdrainages. Later studies have shownthat Pangio fusca is actually restricted

Fig. 11. Pangio aff. fusca, 33 mm SL.Fig. 11. Pangio aff. fusca, 33 mm LS.

to the Salween drainage and Tenas-serim (Myanmar) and that the popula-tions from the Mekong drainage belongto other species (Britz & Maclaine,2007; Britz & Kottelat, 2010). Further, inearlier reports (Kottelat, 2006, 2007),all the Pangio fusca-like fishes of theMekong drainage were believed to be asingle species, although there was asuspicion that more than one specieswere confused under this name (Kotte-lat, 2007). This is now confirmed by arecent and still unpublished study thatdistinguishes three species, diagnosedby morphological as well as molecularcharacters. One of them is known onlyfrom the Nam Theun drainage (calledhere Pangio aff. fusca). Another similarspecies has been observed in the XeBangfai by the 2012 survey (Fig. 12).

The species is very elusive and only12 individuals have been observed, allin 1996. All individuals were observedin localities in the inundation zone, withsoft bottom and/or leave litter, a normalhabitat for species of the genus Pangio.It was also collected at the Nakai Damsite in 1996 and therefore expected forat least some distance in the NamTheun downstream. Some individualshave a very dark colouration and thissuggests that it possibly also inhabitscrevices in rocks, as at the dam site. Insuch habitats they can be very difficult

Fig. 12. The second species of Pangio aff.fusca, from the Xe Bangfai drainage.Fig. 12. La seconde espèce de Pangio aff.fusca, du bassin de la Xe Bangfai.


to collect. The largest number of indi-viduals in a single sample (5) was froma small forest stream near (old) Sop Onvillage, in the inundation zone with softbottom. It is expected to be present insmall, permanent tributaries, with a lowgradient.

There is a number of small forestcreeks entering the Nam Theun betweenthe Nakai Dam and the confluence withthe Nam Phao that could home this spe-cies. On Nakai Plateau, the Nam On,which is inundated only for a shortperiod every year, could also presentsuitable habitats for this species.

Because of its habitat and life habit,the absence of the species in surveysis not conclusive and suggests that thepreferred habitat is missed by the sam-pling methods. Most species of thisgenus burrow in sand or mud and mayescape ichthyocides if they are washedtoo quickly by the current.

6.2.10 Schistura sp. 'Nam Kathang'

Schistura sp. 'Nam Kathang' (Fig. 13)has been observed only in the NamKathang Gnai on Nakai Plateau. TheNam Kathang Gnai is flowing along the

Fig. 13. Schistura sp. 'Nam Kathang'; juvenile,22 mm SL (above) and adult 59 mm SL (below).Fig. 13. Schistura sp. 'Nam Kathang' ; juvénile,22 mm LS (haut) et adulte 59 mm LS (bas).

edge of the plateau but is not a tributaryof the Nam Theun. Instead, it flowsdown the escarpment to the Xe Bangfai.It cannot be identified with any of thespecies known in the Nam Theun andXe Bangfai drainages and is new to sci-ence and named Schistura sp. 'NamKathang' until given a formal name. Thisspecies is not affected by the inundationof the reservoir, but the new BanKhonken village is located on andacross the divide between the NamTheun and Nam Kathang Gnai, andother villages are very close to thedivide, so that disturbance of its habitatby villages is to be expected.

Species of the genus Schisturaoften have small distribution ranges,often limited to a single river drainageor subdrainage. For example mostspecies present in the Nam Theun andNam Gnouang are endemic to theserivers. However, it is not expected thatthis species would be restricted to theNam Kathang Gnai but that it is proba-bly present elsewhere in the Xe Bang-fai drainage, probably together withDevario sp. 'green'.

Schistura sp. 'Nam Kathang' wasobserved at two sites in the NamKathang Gnai, accessed from BanKhonken area, where the stream wasvery narrow and shallow, under forestcover, with a muddy to sand substrate,and Ban Done area where the streamhad been forded, resulting in a deeppool upstream, very slow current andalgae development on the bottom.There, the species was collected in theriffles at the level of the ford, which is thehabitat of most species of Schistura.

Devario sp. 'green' and Schisturasp. 'Nam Kathang' are both known onlyfrom the Nam Kathang Gnai and

26 M. Kottelat

attempts to find them outside the NTPCarea failed. As the species seem to beimpacted by resettlement activities, fur-ther studies are needed to determinetheir endemism. They should includethe search for possible additional pop-ulations outside the Nakai Plateau.

6.2.11 Microcobitis aff. misgurnoides

Microcobitis aff. misgurnoides(Fig. 14) was first discovered during the2007 survey. It is a still unnamed spe-cies related to Microcobitis misgur-noides, a species known only from Cen-tral Vietnam (Rendahl, 1944; Bohlen &Harant, 2011). Morphology and molecu-lar data show that they are distinct spe-cies.

Before inundation, Microcobitis aff.misgurnoides had been observedmostly in shallow lakes on the NakaiPlateau. A few individuals were foundin the Nam Theun and the Nam On, inthe inundation zone. It has never beenobserved further upriver. In 2007, it hasalso been observed in a drying rivernortheast of Laksao, which indicatesthat the species is not endemic to theNakai Plateau.

It is a benthic species, living in softbottom. Most individuals were obtainedin samples that contained Oryzias spe-cies and Esomus metallicus, speciesthat survive the dry season in the worstconditions in dry pools and swamps.

Fig. 14. Microcobitis aff. misgurnoides, 31 mm SL.Fig. 14. Microcobitis aff. misgurnoides, 31 mm LS.

This unpleasant habitat probablyexplains why it had been overlooked.However, it is not restricted to this hab-itat and was also collected in the NamTheun and Nam On rivers at placeswith sand to muddy bottom. In the fieldit is easily confused with Lepidocephal-ichthys hasselti with which it co-occursat all localities, in the same habitat.

Microcobitis aff. misgurnoides isnow present in large numbers in sitesin the inundation zone and is abundantin the mud bottom of pools connectedwith the reservoir at FSL.

6.2.12 Devario aff. quangbinhensis

While searching for Devario sp.'green' in the Xe Bangfai drainage,another species of Devario was col-lected in the Nam Oula catchment(Fig. 15). This species cannot be iden-tified with any of the species known inthe Mekong drainage. It is possibly newto science and has an appearance sim-ilar to that of Devario quangbinhensis,a species described from Vietnam in thedrainage of River Chay, in Quang BinhProvince, which is adjacent to the XeBangfai drainage. The species wasobtained in a small creek in the forestupstream of the limit of that stretch of theNam Oula impacted by the increasedflow and level in the Xe Bangfai.

However, further surveys are neededto determine its endemism. This includes

Fig. 15. Devario aff. quangbinhensis, 75 mm SL.

Fig. 15. Devario aff. quangbinhensis, 75 mm LS.


the search for possible additional pop-ulations in the Xe Bangfai drainage andpossibly in the Xe Banghiang.

6.2.13 Parambassis sp. 'slender'

The Parambassis (Fig. 16) speciesobserved in the Nam Theun and NamGnouang drainages has similaritieswith Parambassis siamensis. However,it is possibly a distinct species becauseof its more elongated body.

This species was first observed inthe Nang Gnouang in 2002 and in theNam Phao in 2007. It was not presentin the samples obtained between 1996and 2009 immediately upstream ofKeng Louang but it was very abundantin 2012 immediately downstream, whereseveral hundreds were seen. Speciesof Parambassis elsewhere inhabit rela-tively slow and standing waters and thedecreased flow in the Nam Theun andstanding water in Theun Hinboun res-ervoir are likely to create more suitableenvironment for this species. Even if itsendemic status is not yet confirmed itseems that no management measure isneeded for this species other than a rou-tine presence monitoring should beundergone in the Nam Theun Riverdownstream.

Fig. 16. Parambassis sp. 'slender', 43 mm SL.Fig. 16. Parambassis sp. 'slender', 43 mm LS.
6.2.14 Oreoglanis lepturus
Oreoglanis lepturus (Fig. 17) is onlyknown from the Nam Phao and mightbe present in the upstream NamGnouang. In the Nam Phao it has beenobserved in 1996 and 2006 only in the1-2 km immediately downstream of theborder between Laos and Vietnam, in astretch with stones and boulders andsmall waterfalls, and in 2012 in theNam Kata, in drying riffles.

Both sites are in sectors veryimpacted by human activity (e.g. irriga-tion network, road construction, goldmining, and fishing). However, the areaswhere the species was observed arenot under the direct influence of theNam Theun 2 project.

6.2.15 Rhinogobius lineatus

Rhinogobius lineatus (Fig. 18) isdefinitively known only from the NamTheun downstream of the Nakai Damand the Nam Gnouang. It was observedin 1996, 2002 and 2009.

The complete range of the speciesis impacted by Nam Theun 2 and TheunHinboun activities. Most of the sites onthe Nam Gnouang are now inundatedby Theun Hinboun extension dam. Onthe Nam Theun, it was present in 2009downstream (Keng Louang, Keng Iru)after completion of the Nakai Dam butwas not seen in 2012.

Fig. 17. Oreoganis lepturus, 53 mm SL.Fig. 17. Oreoganis lepturus, 53 mm LS.

28 M. Kottelat

The genus Rhinogobius was col-lected only once in the Xe Bangfai in2002, close to the downstream entranceof the underground course of the river.Unfortunately this individual was a femaleand thecharactersuseful to identify spe-cies of Rhinogobius are mainly found inmales. This female cannot be reliablyidentified, but it shows similarities withthe females of Rhinogobius lineatus.

Survey should be conducted toobtain more material of the Xe Bangfaiputative population and clarify whetheror not it is Rhinogobius lineatus. Itshould also be searched in the subsist-ing small streams entering the NamGnouang and downstream Nam Theun.Its continued presence in Keng Iru andKeng Louang where it was seen in 2009should be monitored. It is probably alsopresent in the Nam Kading and its trib-utary streams.

7 MODIFICATION OF FISHCOMMUNITIES IN THE NAM THEUN2 PROJECT AREA

7.1 Upper Nam Theun

Sampling was conducted in theupper Nam Theun in 1996, 2003, 2006

Fig. 18. Rhinogobius lineatus; male, 36 mm SL(above) and female, 37 mm SL (below).Fig. 18. Rhinogobius lineatus ; mâle, 36 mm LS(haut) et femelle, 37 mm LS (bas).

and 2012; several sites were visitedtwice and one site was visited 3 times.In 2012, the situation of the aquatichabitats in the upstream Nam Theunabove FSL has not changed signifi-cantly since the original 1996 survey.However the human population hasincreased and is more present alongthe river, with more houses and newhamlets. The river morphology doesnot seem to have changed although atleast one site that earlier was a sandbank had become a bar of boulders,which seems a natural process, possi-bly the result of the 2011 storms.

No difference in the number of spe-cies and the composition of the fishcommunities was observed. This wasexpected since this stretch of the riveris entirely within the NPA. However, thenumber of fish individuals seems lowerand the size of the fishes seemssmaller, suggesting overfishing.

The species diversity at the upper-most point that can be reached by boatwas comparable to that of previousyears: 23 species collected in 2012, 18in 2006, 26 in 2003. But compared toearlier years, there was no large fish in2012. Although no conclusion can bereached from a single sampling, thismight reflect an increased fishing pres-sure. It might as well reflect that at thissite the water was shallower and flow-ing over a much wider bed while in theprevious years the rapids were nar-rower and deeper. Increased fishingpressure was also reported to be thecause of the rarefaction of large individ-uals of Luciocyprinus striolatus.

7.2 Nakai Plateau

The Nakai Plateau being nowalmost totally inundated part of the


year, the riverine species, and espe-cially the rheophilic ones, have disap-peared. The species inhabiting theswamps are still present. Two are veryabundant (Oryzias sp. 'river', Microco-bitis aff. misgurnoides). A third one(Oryzias sp. 'swamp') was present inlarge numbers before inundation but isnow rare and localised.

7.3 Lower Nam Theun

The closing of Nakai Dam resultedin a very reduced flow most of the year(2 m3/s), and without variation. Parts ofthe rapids are now exposed, sandbanks have become more extensive,etc. The species most specialised forrheophilic habitats become rarer andsome are expected to disappear.Native species requiring slower water(e.g. Parambassis sp. 'slender') orsandy bottoms (e.g. Nemacheilus are-nicolus) become more abundant.

The Keng Louang rapids on thelower Nam Theun were sampled in1996, 2006, 2007, 2009 and 2012. Thefirst four samples were obtained atexactly the same location. In 2012, thewater level was so low that the rivercould be crossed in stepping fromstone to stone; the earlier sampling sitewas exposed and another site had tobe selected, not totally equivalent.Table III shows the species collected atKeng Louang in 1996, 2006 and 2007before closure of the dam, and 2009and 2012 after closure. The 2006 sam-ple is indicative only; the identificationswere based on field observations (thecourier company destroyed the sample).The list of species shows great varia-tion between the years. The 1996-2009

samples included 10 to 16 species,while the 2012 sample includes 23 spe-cies.

Five of the species observed in 2012and absent in the samples of the previ-ous years prefer slow flowing or evenstanding water (Cyclocheilichthys arma-tus, Esomus metallicus, Nemacheilusarenicolus, Parambassis sp. 'slender',Puntius brevis). Three species presentin 2012 but not recorded earlier are spe-cialist of fast waters (Garra cyrano,Balitoropsis yunnanensis, Schisturaatra). A single species was present in allfive samples (Poropuntius carinatus).Opsarius pulchellus was present in allprevious samples but missing in 2012.

In the 2009 sample, 4 out of 14 spe-cies also had not been observed beforeand they were also species not usuallyassociated with rapids (Devario fang-fangae, Hemiculterella macrolepis, Neo-dontobutis aurarmus, Rasbora paviana).In 2009, two species typical of rapidsand observed in all previous sampleswere missing (Garra theunensis,Scaphiodonichthys acanthopterus).

A variation in the presence/absenceor abundance of a species is normaland expected. The differences betweenthe samples, however, is partly explainedby the different location and differentmorphology of the sampling sites. The2012 downstream site included a poolwith little current at the time of the visit.Apparently this also confirms a shifttowards a less rheophilic fish communityalready observed in 2009 after the clo-sure of the Nakai Dam and the lowerand extended dry season release.There is also indication that speciesfrom very slow or standing water ofTheun-Hinboun reservoir may now beable to invade the lower Nam Theun. It

30 M. Kottelat

Table III. Fish species collected in downstream Nam Theun at Keng Louang rapids between 1996 and2012. Note: identifications for sample 2006 are based on field notes and the list is probably incomplete(see text). Samples from 1996 to 2009 were obtained at the same location at the upper edge of therapids; in 2012 this point was emerged and the sample was obtained at mid height of the rapids.Tableau III. Espèces de poissons de poissons récoltées dans la Nam Theun inférieure, aux rapides deKeng Louang entre 1996 et 2012. Note : les identifications de l'échantillonnage de 2006 sont basées surles notes de terrain et sont probablement incomplètes (voir texte). Les échantillons de 1996 à 2009 ontété obtenus au même emplacement au bord supérieur des rapides ; en 2012 cet emplacement étaitémergé et l'échantillon a été obtenu à mi-hauteur des rapides.

Species 1996 2006 2007 2009 2012Balitora lancangjiangensis x xBalitoropsis yunnanensis xCirrhinus molitorella xCycloceilichthys armatus xDevario fangfangae xEsomus metallicus xGarra cambodgiensis x x x xGarra cyrano xGarra theunensis x x x xGlyptothorax laosensis x xGlyptothorax horai x xGlyptothorax aff. zanaensis x x xGyrinocheilus aymonieri x x xHampala macrolepidota xHeminagrus wyckioides x xHemiculterella macrolepis xHemimyzon papilio xHomalopteroides smithi x x xMastacembelus armatus x xMystacoleucus marginatus x xNemacheilus arenicolus xNeodontobutis aurarmus xOnychostoma fusiforme xOpsarius pulchellus x x x xPapuligobius ocellatus x x x xParambassis sp. 'slender' xPoropuntius carinatus x x x x xPuntius brevis xRasbora paviana x xRhinogobius lineatus xScaphiodonichthys acanthopterus x x x xSchistura atra xSchistura cataracta x x x xSchistura kongphengi x xSchistura obeini xTor tambra x xTotal 10 10 16 14 23


also cannot be excluded that some ofthese species were not native but intro-duced in Theun Hinboun Reservoir.

7.4 Nam Phao

The Nam Phao (and its branch NamKata) is the only tributary of the NamTheun downstream of Nakai Dam. Itwas expected that these rivers couldserve as refuges for juvenile and small-sized species. Unfortunately, thesetributaries suffer great anthropogenicimpacts. Some have been observedsince the beginning of the monitoring in1996 (e.g. the formation of large sandbanks and filling of all deep holes of theNam Phao, a result of the constructionof a small dam upstream of Laksao andof road work). The number of speciesobtained by the 2012 survey and thenumber and size of the individualsseems lower. The number of samplesis probably too low to reach an objec-tive conclusion.

The situation of the Nam Kata did notdiffer between 2002 and 2012 in the vis-ited stretch. The Nam Kata suffers ofstrong sedimentation and is heavilyimpacted by mining and the related pol-lution, water abstraction, eutrophica-tion, and possibly pesticides. At eachvisit, the fish densities were low and thefish collected were all juveniles or aresmall-sized species.

7.5 Downstream Xe Bangfai

The modified water conditions makeit impossible to replicate the samplingdone in 1996 and 2006. In addition sam-pling in the Xe Bangfai itself is now

much more difficult because of thehigher water level and greater dis-charge. Effective sampling in the riveritself is possible only with the localseines and local population. In 2012,suitable conditions were present in BanBoungxe, a site already sampled in2006.

In 2012, 28 fish species wereobtained in water less than about 2meters deep, by seine over sandy bot-tom. This compares with 25 speciesobtained in 2006 in the same area. Inthe same area, the 1996 sampling hadyielded 40 species near the confluencewith the Mekong and 38 on a 7-kmstretch downstream of the bridge atBan Khouaxe. The combined totalnumber of species of these two sam-ples was 57. The number of specieswas considerably higher but the 1996samples involved more workers, longerseines (200 m vs. 50 m), lasted a wholeday each, and included various habi-tats (mud, clay, sand, gravel bar, back-waters etc.) while only sand was avail-able at the site sampled in 2012.

Nine species out of 28 (32%)obtained at the 2012 site had not beenobserved in the same area by the 1996and 2006. Among them, 4 species hadnot been recorded in the Xe Bangfaibefore, and one (Acantopsis sp. 'dwarfmales') is possibly new to science.

That a single sample in 2012included 1/3 of species not observedbefore in that part of the river with asimilar methodology indicates that thefish fauna of the lower part of the riveris still undersampled, that more sam-pling should be conducted. In fact thevarious surveys have taken only 7samples in the Xe Bangfai itself down-stream of the bridge (Ban Khouaxe)

32 M. Kottelat

between 1996 and 2012. It is alsoexpected that sampling at the samesite at different times of the year wouldyield different species. Sampling bynight would also add a number of spe-cies, especially catfishes.

No conclusion on the impact ofNTPC activity on the fish diversity ofthat stretch of the Xe Bangfai can bederived from this sampling.

Two samples were obtained in theXe Noy, a main tributary of the Xe Bang-fai, at and above the maximum extent ofthe water backed up by the increasedflow of the Xe Bangfai. A combined totalof 48 species was obtained. Theobserved fish community is represent-ative of what was known in the Xe Bang-fai in similar habitats between Mahaxaiand the confluence with the Nam Phit.

8 DISCUSSION – CONCLUSION

8.1 Fish biodiversity

Detailed surveys before construc-tion allowed to identify the biodiversityimportant species and to focus atten-tion on them during monitoring.

The fish fauna of the Nam Theunand the Xe Bangfai are strikingly differ-ent. There is an obvious difference inrichness, with 74 native species in theNam Theun drainage and 178 in the XeBangfai drainage. Part of the differenceresults from the different purposes ofthe various samplings, which imposedpriorities and geographical limits: whilethe Xe Bangfai was surveyed for itswhole length, from the headwaters tothe Mekong, the Nam Theun is only theupper part of the Nam Kading drainageand no lowland and floodplain habitats

were included in the surveys. On thereverse, the coverage for the upper partof the Xe Bangfai is very limited and thesampling on the whole river was lessdense than on the Nam Theun.

Despite these reservations, our sur-veys show that the Nam Theun hasfewer species than the Xe Bangfai butthat 21 (28%) of the 74 native speciesare endemic. It might be that some ofthese species await to be discovered inother tributaries of Nam Kading and inthe Nam Xan drainage north of theNam Theun. Besides, as mentionedabove, a number of species of the NamTheun are closely related with speciesand genera otherwise known only fromthe other side of the Annamite Rangeand unknown or with very restrictedranges in the Mekong drainage. Thefauna of the Nam Theun has more sim-ilarities with that of the drainages to thenorth.

On the other hand, only 9 (5%) ofthe 178 species reported from the XeBangfai are endemic. The Xe Bangfaifish fauna is similar to the fauna of theMekong major tributaries to the South,in Laos and Thailand. Three of the'endemics' were discovered by the2012 survey in habitats still insuffi-ciently sampled in other drainages andsome are expected to be discoveredthere too.

The majority of the Nam Theun fishspecies inhabit rapids and very fastwaters (rheophilic habitats), with some(Oreoglanis spp., Pseudecheneis sym-pelvica) present even in waterfalls.Many of these species have developedstructures that allow them to keep posi-tion in strong current, like laterallyexpanded fins, fins fused to form asucker, sucking mouth, gill opening


modification allowing to inhale andexhale water, tubercles on the snout toreduce the pressure of the current,jaws with a sharp cutting edge toscrape algae from the surface of thestones, skin lamellae on the belly witha structure similar to the sucking disk ofremoras, etc. The Xe Bangfai has veryfew species with such structures (butthis may partly reflect that suitable hab-itats could not be reached).

To date, a single species of the XeBangfai is also known, or is closelyrelated to a species, from the otherslope of the Annamite Range in Vietnam(Devario aff. quangbinhensis), althoughthe divide between the two slopes isvery low (about 400 masl).

The swamp and marsh habitats ofthe Nam Theun and Xe Bangfai drain-ages also differ conspicuously. Theswamp habitats of the Xe Bangfai arein the Mekong floodplain and have arich fauna, made mostly of speciespresent throughout the floodplain of themiddle Mekong, with no endemic. Onthe other hand, the swamp habitats inthe Nam Theun are located on NakaiPlateau. They are fed by rain and bythe cool water of the Nam Theun. Theyhave a very small number of speciesbut three of them are endemic, and twoonly known from the inundation zone.

8.2 Status of Nam Theun endemicfishes

The construction of dams and reser-voirs unavoidably has severe impactson aquatic habitats and aquatic biodi-versity. The impact on rheophilic spe-cies could be a serious issue becausethese species not only have a limited

distribution within a drainage, but alsobecause the ranges of rheophilic spe-cies are restricted to a few or a singledrainage. Because of its morphology,the Nam Theun has a fauna mostly rhe-ophilic (38 out of 74 species), of which13 (34%) are endemic (or endemic tothe Nam Theun + Nam Gnouang). Inother words, 1/6 of the fish species ofthe Nam Theun were potentially threat-ened of extinction by the project.

The rivers upstream of the NakaiReservoir are large and diverse enoughto provide habitats to all but two of theendemic rheophilic species. Thesehabitats are within the NPA and there-fore supposedly safe at the short andmedium term. Since no long-distancemigratory species was found (and nonewas reported by the local population)the dam is not a barrier threatening thelife cycle of any migratory species. Fur-ther, downstream of Nakai Reservoir,the river was already blocked by Theun-Hinboun Dam.

The future of one rheophilic speciesnot observed upstream of the reservoir(Scaphognathops theunensis) is dim-mer. At the time the surveys were con-ducted, a significant share of its rangewas in the Nam Gnouang and itseemed to be reasonably safe. How-ever, between the time the surveyswere conducted and the constructionof the Nakai Dam, an extension damfor the Theun-Hinboun Reservoir wasbuilt on the Nam Gnouang, flooding theremaining intact habitat of the species.This underlines the need of a basin-wide management of aquatic biodiver-sity. The other endemic rheophilic spe-cies not present upstream of NakaiReservoir (Rhinogobius lineatus) is asmaller fish with different habitat

34 M. Kottelat

requirements. Although still a biodiver-sity important species, it seems in asafer situation with its range apparentlyextending above FSL of the Theun-Hinboun extension Reservoir.

The rivers in the NPA are presentlythe best known remaining habitat forthe endangered Luciocyprinus striola-tus and potentially the only one wherethe species has chances to survive.This assumes that the aquatic habitatsbe managed with the same attention asterrestrial habitats.

While most of the original habitat ofthe species endemic to the swamps ofNakai Plateau is inundated, two areabundant along the shores of the reser-voir and do not seem of concern. Thethird one (Oryzias sp. 'swamp') hadbecome very rare and has now beenrediscovered and is the subject of spe-cific studies and its future is nowexpected to be safer.

The status of Rhodeus laoensis isnot clear. It has been recordedupstream of Nakai Reservoir, but onlyjuveniles and at low density. The sup-posed host mussel is rare and inplaces in the NPA where juvenile bit-terlings had been collected the villag-ers were not even aware of the pres-ence of mussels. The two speciesneed more attention. The objectiveidentification of the host is needed (byconfirming the presence of fish larvaein the mussel).

To conclude, the survival of some ofthe endemic species may require addi-tional measures, such as establishingconservation zones and specific fishingregulations. Obviously, this can be suc-cessful only with communication withthe local population.

ACKNOWLEDGMENTS

The research summarised hereresults from several surveys conductedfor the Nam Theun 2 Power Company(NTPC) in Lao PDR whose sharehold-ers are Electricité de France, Lao Hold-ing State Enterprise, and ElectricityGenerating Public Company Limited ofThailand.

Over the year, I benefitted from thesupport of many managers and staff ofNTPC, especially in the early yearsFrançois Obein and Peter Goldston.Likewise, the field work would not havebeen successful without the assistanceof a great number of villagers, localworkers,NTPCstaff (especiallyPhoutha-kone Luangyotha, Stuart Gillon, Kham-keng Yuena), researchers and staffof LARREC (Kongpheng Boua-khamvongsa, Sinthawong Viravong,Khamtanh Vatthanatham) and othercollaborators (Soutchai Khamphousay,Tan Heok Hui, Leong Tzi Ming). I thankKatsuma Kubota (Bangkok) for provid-ing information on spawning of Oryziassp. 'swamp'; Arthur E. Bogan (NorthCarolina State Museum of Natural Sci-ences, Raleigh) for identification of themussels; Liankham Payasane (NTPC)for designing the map; and Maud Cottet(NTPC) for various information anddata and for her help to organise andfinalise this article.

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(Teleostei: Gobiidae). IchthyologicalExploration of Freshwaters 11(1) : 81-87.

Chen I.-S., Kottelat M. & Miller P. J., 1999.Freshwater gobies of the genus Rhino-gobius from the Mekong basin in Thai-land and Laos, with descriptions of threenew species. Zoological Studies 38(1) :19-32.

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Fang F. & Kottelat M., 1999. Danio speciesfrom northern Laos, with descriptions ofthreenewspecies (Teleostei:Cyprinidae).Ichthyological Exploration of Freshwa-ters 10(3) : 281-295.

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Kottelat M., 1997. Distribution of the fishespreviously considered endemic to theNam Theun and Xe Bangfai basins, LaoP.D.R. Report prepared for Nam Theun2 Electricity Consortium, Vientiane.

Kottelat M., 1998. Fishes of the Nam Theunand Xe Bangfai basins, Laos, with dia-gnoses of twenty-two new species(Teleostei: Cyprinidae, Balitoridae,Cobitidae, Coiidae and Odontobutidae).Ichthyological Exploration of Freshwa-ters 9(1) : 1-128.

Kottelat M., 2000. Diagnoses of a newgenus and 64 new species of fishesfrom Laos (Teleostei: Cyprinidae, Balito-ridae, Bagridae, Syngnathidae, Chaud-huriidae and Tetraodontidae). Journal ofSouth Asian Natural History 5(1) : 37-82.

Kottelat M., 2001. Fishes of Laos. WildlifeHeritage Trust. Colombo: 198 p.

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Kottelat M. & Steiner H., 2011. Banganamusaei, a new cave fish from centralLaos (Teleostei: Cyprinidae). Ichthyolo-gical Exploration of Freshwaters 21(4) :313-322.

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Ng H.H., 1999b. Laides longibarbis, a validspecies of schilbeid catfish from Indo-china (Teleostei: Siluriformes). Ichthyo-logical Exploration of Freshwaters10(4) : 381-385.

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Ng H.H. & Kottelat M., 1999. Oreoglanishypsiurus, a new species of glyptoster-nine catfish (Teleostei: Sisoridae) fromLaos. Ichthyological Exploration ofFreshwaters 10(4) : 375-380.

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38 M. Kottelat

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eM

ekon

gba

sin

Ost

eoch

ilus

vitta

tus

*x

Sou

thea

stA

sia

Ost

eoch

ilus

waa

nder

sii

xS

outh

east

Asi

a


pp

end

ix1.

Con

tinue

d.

An

nex

e1.

Sui

te.

Xe

Ban

gfa

iN

amT

heu

nD

istr

ibu

tio

no

uts

ide

Xeb

ang

faia

nd

Nam

Th

eun

(raw

ou

tlin

e)lo

wer

mid

dle

up

per

low

erp

late

auu

pp

erh

ead

wat

ers

Cyp

rin

idae

(con

tinue

d)O

xyga

ster

poin

toni

xM

ekon

gan

dC

hao

Phr

aya

basi

nsP

arac

hela

oxyg

astr

oide

sx

Sou

thea

stA

sia

Par

ache

lasi

amen

sis

xM

ekon

gan

dC

hao

Phr

aya

basi

nsP

aral

aubu

caba

rron

ix

Mek

ong

basi

nP

aral

aubu

cariv

eroi

xM

ekon

gan

dC

hao

Phr

aya

basi

nsP

aral

aubu

caty

pus

xx

Mek

ong

and

Cha

oP

hray

aba

sins

Por

opun

tius

carin

atus

xx

xx

Mek

ong

basi

nP

orop

untiu

sla

oens

isx

xx

Mek

ong

basi

nP

orop

untiu

sno

rman

ix

Mek

ong

basi

nP

roba

rbus

labe

amin

orx

Mid

dle

Mek

ong

basi

nP

untio

plite

sfa

lcife

rx

xx

Mek

ong

basi

nP

untiu

sbr

evis

xS

outh

east

Asi

aR

aiam

asgu

ttatu

sx

xx

xx

Mai

nlan

dS

outh

east

Asi

aR

asbo

raat

ridor

salis

xM

ekon

gba

sin

inY

unna

nR

asbo

rabo

rape

tens

isx

xM

ainl

and

Sou

thea

stA

sia

Ras

bora

dani

coni

usx

Mai

nlan

dS

outh

east

Asi

aan

dS

outh

Asi

aR

asbo

ram

yers

i*x

xS

outh

east

Asi

aR

asbo

rapa

vian

ax

xx

xx

Mai

nlan

dS

outh

east

Asi

aR

asbo

raat

ridor

salis

xM

ekon

gan

dC

hao

Phr

aya

drai

nage

sR

asbo

ratr

iline

ata

xx

Sou

thea

stA

sia

Rho

deus

laoe

nsis

*x

xx

Nam

The

unen

dem

icS

caph

iodo

nich

thys

acan

thop

teru

sx

xx

xx

xM

ekon

gan

dC

hao

Phr

aya

basi

nsS

caph

ogna

thop

sba

ndan

ensi

sx

xM

ekon

gba

sin

Sca

phog

nath

ops

stej

nege

rix

xM

ekon

gba

sin

Sca

phog

nath

ops

theu

nens

is*

xx

Nam

The

un-

Nam

Gno

uang

ende

mic

Sik

ukia

gudg

eri

xx

Mek

ong

and

Cha

oP

hray

aba

sins

Tor

ater

xN

amT

heun

ende

mic

44 M. Kottelat

Ap

pen

dix

1.C

ontin

ued.

An

nex

e1.

Sui

te.

Xe

Ban

gfa

iN

amT

heu

nD

istr

ibu

tio

no

uts

ide

Xeb

ang

faia

nd

Nam

Th

eun

(raw

ou

tlin

e)lo

wer

mid

dle

up

per

low

erp

late

auu

pp

erh

ead

wat

ers

Cyp

rin

idae

(con

tinue

d)T

orla

teriv

ittat

us*

xx

xx

Mek

ong

basi

nT

orta

mbr

ax

Sou

thea

stA

sia

Tor

tam

broi

des

xx

Sou

thea

stA

sia

Gyr

ino

chei

lidae

Gyr

inoc

heilu

say

mon

ieri

xx

xM

ainl

and

Sou

thea

stA

sia

Bal

ito

rid

aeA

nnam

iano

rman

ix

Ann

amite

Ran

geB

alito

racf

.ann

amiti

cax

Xe

Kon

gba

sin

inC

ambo

dia

Bal

itora

lanc

angj

iang

ensi

sx

xx

Mek

ong

and

Red

Riv

erba

sins

inY

unna

nB

alito

rops

isse

xmac

ulat

a*

xB

alito

rops

isyu

nnan

ensi

s*

xx

xx

Mek

ong

basi

nH

emim

yzon

papi

lio*

xx

xM

iddl

eM

ekon

gba

sin

Hom

alop

tero

ides

smith

i*x

xx

xx

xM

ainl

and

Sou

thea

stA

sia

Nem

ach

eilid

aeN

emac

heilu

sar

enic

olus

*x

xx

xN

amT

heun

ende

mic

Nem

ache

ilus

long

istr

iatu

sx

xM

ekon

gba

sin

Nem

ache

ilus

palli

dus

xx

Mek

ong

and

Cha

oP

hray

aba

sins

Nem

ache

ilus

plat

icep

sx

xM

ekon

gba

sin

inC

ambo

dia

Sch

istu

raat

ra*

xx

xN

amT

heun

ende

mic

Sch

istu

rada

uben

toni

xM

ekon

gba

sin

inC

ambo

dia

and

Sou

ther

nLa

osS

chis

tura

cata

ract

ax

xx

Nam

The

unen

dem

icS

chis

tura

dors

izon

a*

xx

xM

iddl

eM

ekon

gba

sin

Sch

istu

rais

ostig

ma

*x

Mid

dle

Mek

ong

basi

nS

chis

tura

kong

phen

gi*

xx

xM

iddl

eM

ekon

gba

sin

Sch

istu

rani

chol

six

xM

ekon

gba

sin

Sch

istu

ranu

dido

rsum

*x

xN

amT

heun

ende

mic

Sch

istu

raob

eini

*x

xx

xN

amT

heun

ende

mic


pp

end

ix1.

Con

tinue

d.A

nn

exe

1.S

uite

.

Xe

Ban

gfa

iN

amT

heu

nD

istr

ibu

tio

no

uts

ide

Xeb

ang

faia

nd

Nam

Th

eun

(raw

ou

tlin

e)lo

wer

mid

dle

up

per

low

erp

late

auu

pp

erh

ead

wat

ers

Nem

ach

eilid

ae(c

ontin

ued)

Sch

istu

rapu

nctif

asci

ata

*x

xX

eB

angf

aien

dem

icS

chis

tura

som

boon

i*x

xx

xM

iddl

eM

ekon

gba

sin

Sch

istu

ratu

bulin

aris

*x

xN

amT

heun

ende

mic

Sch

istu

rasp

.'N

amK

atha

ng'

xX

eB

angf

aien

dem

icC

ob

itid

aeA

cant

hops

oide

sde

lpha

xx

Mek

ong

and

Cha

oP

hray

aba

sins

Aca

ntho

psoi

des

grac

ilent

usx

Mek

ong

basi

nA

cant

hops

oide

sha

palia

sx

xM

ekon

gba

sin

Aca

ntop

sis

sp.'

dwar

fmal

es'

xX

eB

angf

aien

dem

ic?

Aca

ntop

sis

sp.'

larg

esp

ots'

xM

ekon

gan

dC

hao

Phr

aya

basi

nsA

cant

opsi

ssp

.'sm

alls

pots

'x

xM

ainl

and

Sou

thea

stA

sia

Aca

ntop

sis

sp.'

vert

ical

spot

s'x

Xe

Ban

gfai

ende

mic

?Le

pido

ceph

alic

hthy

sfu

rcat

usx

Mai

nlan

dS

outh

east

Asi

aLe

pido

ceph

alic

hthy

sha

ssel

tix

xx

Mai

nlan

dS

outh

east

Asi

aLe

pido

ceph

alic

hthy

sze

ppel

ini

xM

ekon

gba

sin

Mic

roco

bitis

aff.

mis

gurn

oide

sx

xN

amT

heun

-Nam

Gno

uang

ende

mic

Mis

gurn

usan

guill

icau

datu

sx

xE

astA

sia

Pan

gio

aff.

angu

illar

isx

xM

ekon

gba

sin

Pan

gio

aff.

fusc

aN

amT

heun

xx

Nam

The

unen

dem

ic?

Pan

gio

aff.

fusc

aX

eB

angf

aix

Mek

ong

basi

nS

erp

enti

cob

itid

aeS

erpe

ntic

obiti

szo

nata

*x

Mid

dle

Mek

ong

basi

nB

oti

idae

Am

bast

aia

nigr

olin

eata

*x

xM

ekon

gan

dC

hao

Phr

aya

basi

nsS

yncr

ossu

sbe

aufo

rti*

xx

xM

ainl

and

Sou

thea

stA

sia

Syn

cros

sus

helo

des

*x

Mek

ong

and

Cha

oP

hray

aba

sins

Yas

uhik

otak

iaca

udip

unct

ata

*x

Mek

ong

basi

nY

asuh

ikot

akia

eos

*x

xM

ekon

gba

sin

Yas

uhik

otak

iale

cont

ei*

xM

ekon

gba

sin

46 M. Kottelat

Ap

pen

dix

1.C

ontin

ued.

An

nex

e1.

Sui

te.

Xe

Ban

gfa

iN

amT

heu

nD

istr

ibu

tio

no

uts

ide

Xeb

ang

faia

nd

Nam

Th

eun

(raw

ou

tlin

e)lo

wer

mid

dle

up

per

low

erp

late

auu

pp

erh

ead

wat

ers

Bo

tiid

ae(c

ontin

ued)

Yas

uhik

otak

ialo

ngid

orsa

lisx

Mek

ong

basi

nY

asuh

ikot

akia

mod

esta

*x

Mek

ong

and

Cha

oP

hray

aba

sins

Bag

rid

aeH

emib

agru

sne

mur

usx

xS

outh

east

Asi

aH

emib

agru

sfil

amen

tus

xM

ekon

gba

sin

Hem

ibag

rus

wyc

kioi

des

xM

ekon

gba

sin

Mys

tus

atrif

asci

atus

xx

Mek

ong

and

Cha

oP

hray

aba

sins

Mys

tus

mys

ticet

usx

Mek

ong

and

Cha

oP

hray

aba

sins

Mys

tus

sing

arin

gan

xx

Sou

thea

stA

sia

Pse

udom

ystu

ssi

amen

sis

xx

xx

Mai

nlan

dS

outh

east

Asi

aA

mb

lyci

pit

idae

Am

blyc

eps

serr

atum

*x

xLo

wer

Mek

ong

basi

nS

iluri

dae

Bel

odon

ticht

hys

trun

catu

sx

Mai

nlan

dS

outh

east

Asi

aK

rypt

opte

rus

bici

rrhi

sx

Sou

thea

stA

sia

Kry

ptop

teru

scr

ypto

pter

usx

xS

outh

east

Asi

aM

icro

nem

aap

ogon

*x

Sou

thea

stA

sia

Mic

rone

ma

chev

eyi*

xM

ekon

gan

dC

hao

Phr

aya

basi

nsP

tero

cryp

tisin

usita

ta*

?x

xx

Nam

The

un+

Nam

Gno

uang

ende

mic

Sch

ilbid

aeLa

ides

long

ibar

bis

xM

ainl

and

Sou

thea

stA

sia

Pan

gas

iidae

Pan

gasi

usla

rnau

dii

xM

ekon

gan

dC

hao

Phr

aya

basi

nsC

lari

idae

Cla

rias

batr

achu

sx

xx

xS

outh

east

Asi

aS

iso

rid

ae

Bag

ariu

sya

rrel

lix

xS

outh

east

and

Sou

thA

sia

Gly

ptot

hora

xaf

f.fu

scus

1*

xx

xM

ekon

gba

sin

?


pp

end

ix1.

Con

tinue

d.

An

nex

e1.

Sui

te.

Xe

Ban

gfa

iN

amT

heu

nD

istr

ibu

tio

no

uts

ide

Xeb

ang

faia

nd

Nam

Th

eun

(raw

ou

tlin

e)lo

wer

mid

dle

up

per

low

erp

late

auu

pp

erh

ead

wat

ers

Sis

ori

dae

(con

tinue

d)

Gly

ptot

hora

xaf

f.fu

scus

2X

eB

angf

aien

dem

ic?

Gly

ptot

hora

xho

rai*

xx

xx

Mek

ong

basi

nG

lypt

otho

rax

laos

ensi

sx

xx

xM

ekon

gan

dC

hao

Phr

aya

basi

nsG

lypt

otho

rax

aff.

zana

ensi

sx

Sal

wee

nan

dM

ekon

gba

sins

Ore

ogla

nis

hyps

iuru

s*

xx

Nam

The

unen

dem

icO

reog

lani

sle

ptur

us*

xx

Nam

The

unen

dem

icP

seud

eche

neis

sym

pelv

ica

*x

Mid

dle

Mek

ong

basi

nA

kysi

idae

Aky

sis

iner

mis

xM

iddl

eM

ekon

gba

sin

Aky

sis

variu

s*

xx

Mid

dle

Mek

ong

basi

nS

ynb

ran

chid

aeM

onop

teru

sja

vane

nsis

*x

xx

Sou

thea

stA

sia

Ad

rian

ich

thyi

dae

Ory

zias

mek

onge

nsis

xM

ekon

gba

sin

Ory

zias

pect

oral

isx

Nam

The

unen

dem

icO

ryzi

assp

.'riv

er'*

xN

amT

heun

ende

mic

Ory

zias

sp.'

swam

p'*

xN

amT

heun

ende

mic

Bel

on

idae

Xen

ento

don

canc

iloid

es*

xx

Mai

nlan

dS

outh

east

Asi

aS

yng

nat

hid

aeD

oryi

chth

ysco

ntig

uus

*x

Sou

thea

stA

sia

Am

bas

sid

aeP

aram

bass

issi

amen

sis

xx

Mai

nlan

dS

outh

east

Asi

aP

aram

bass

issp

.'sl

ende

r'x

Nam

The

un-

Nam

Gno

uang

ende

mic

?T

oxo

tid

aeT

oxot

esm

icro

lepi

sx

Sou

thea

stA

sia

Nan

did

aeN

andu

sox

yrhy

nchu

sx

Mek

ong

basi

n

48 M. Kottelat

Ap

pen

dix

1.C

ontin

ued.

An

nex

e1.

Sui

te.

Xe

Ban

gfa

iN

amT

heu

nD

istr

ibu

tio

no

uts

ide

Xeb

ang

faia

nd

Nam

Th

eun

(raw

ou

tlin

e)lo

wer

mid

dle

up

per

low

erp

late

auu

pp

erh

ead

wat

ers

Pri

sto

lep

idid

aeP

risto

lepi

sfa

scia

tax

xS

outh

east

Asi

aD

atn

ioid

idae

Dat

nioi

des

unde

cim

radi

atus

*x

xM

ekon

gba

sin

Od

on

tob

uti

dae

Neo

dont

obut

isau

rarm

us*

xx

xx

Mek

ong

basi

nT

erat

eleo

tris

aspr

o*

xX

eB

angf

aien

dem

icE

leo

trid

idae

Oxy

eleo

tris

mar

mor

ata

xS

outh

east

Asi

aG

ob

iidae

Bra

chyg

obiu

sm

ekon

gens

isx

Mek

ong

basi

nG

obio

pter

usch

uno

xM

ekon

gba

sin

Pap

ulig

obiu

soc

ella

tus

*x

xx

xx

Mek

ong

basi

nR

hino

gobi

uslin

eatu

s*

xN

amT

heun

-N

amG

noua

ngen

dem

icA

nab

anti

dae

Ana

bas

test

udin

eus

xx

Sou

thea

stan

dS

outh

Asi

aO

sph

ron

emid

aeB

etta

smar

agdi

nax

xM

ekon

gba

sin

Osp

hron

emus

exod

onx

Mek

ong

basi

nT

richo

podu

str

icho

pter

us*

xS

outh

east

Asi

aT

richo

psis

scha

lleri

*x

xx

Mek

ong

basi

nT

richo

psis

vitta

tax

Sou

thea

stA

sia

Ch

ann

idae

Cha

nna

gach

uax

xx

xx

Sou

thea

stan

dS

outh

Asi

aC

hann

aaf

f.m

arul

ius

xM

ekon

gba

sin

Cha

nna

mic

rope

ltes

xS

outh

east

Asi

aC

hann

ast

riata

xx

xx

Sou

thea

stan

dS

outh

Asi

aC

hau

dh

uri

idae

Cha

udhu

riaca

udat

ax

Mai

nlan

dS

outh

east

Asi

a


Ap

pen

dix

1.C

ontin

ued.

An

nex

e1.

Sui

te.

Xe

Ban

gfa

iN

amT

heu

nD

istr

ibu

tio

no

uts

ide

Xeb

ang

faia

nd

Nam

Th

eun

(raw

ou

tlin

e)lo

wer

mid

dle

up

per

low

erp

late

auu

pp

erh

ead

wat

ers

Ch

aud

hu

riid

ae(c

ontin

ued)

Cha

udhu

riafu

sipi

nnis

xM

ekon

gba

sin

Mas

tace

mb

elid

aeM

acro

gnat

hus

sem

ioce

llatu

sx

Mek

ong

and

Cha

oP

hray

aba

sins

Mac

rogn

athu

ssi

amen

sis

xx

Mek

ong

and

Cha

oP

hray

aba

sins

Mas

tace

mbe

lus

arm

atus

*x

xx

xx

xx

Sou

thea

stan

dS

outh

Asi

aS

ole

idae

Bra

chiru

sha

rman

di*

xx

Mek

ong

and

Cha

oP

hray

aba

sins

Tet

rao

do

nti

dae

Aur

iglo

bus

nefa

stus

xS

outh

east

Asi

aP

aoab

ei*

xx

xM

ekon

gan

dN

anba

sins

Pao

coch

inch

inen

sis

*x

Mai

nlan

dS

outh

east

Asi

aP

aosu

vatti

i*x

xM

ekon

gba

sin

Pao

turg

idus

*x

Mid

dle

Mek

ong

basi

n

50 M. Kottelat

Appendix 2. Species appearing under a different name in earlier reports, publication and in Kottelat(2001).Annexe 2. Espèces apparaissant sous un nom différent dans de précédents rapports, publication etdans Kottelat (2001).

Present name Earlier name

Akysis varius Akysis sp. n. aff. heterurus

Ambastaia nigrolineata Botia cf. nigrolineata, Yasuhikotakia nigrolineata

Amblyceps serratum Amblyceps sp. n. aff. mangois

Bangana elegans Bangana sp. n. aff. sinkleri

Barbodes aurotaeniatus Puntius aurotaeniatus

Barbodes jacobusboehlkei Puntius jacobusboehlkei

Barbodes rhombeus Puntius rhombeus

Barbonymus altus Barbodes altus

Barbonymus gonionotus Barbodes gonionotus

Barbonymus schwanenfeldii Barbodes schwanenfeldii

Brachirus harmandi Euryglossa harmandi

Crossocheilus oblongus Crossocheilus siamensis

Datnioides undecimradiatus Coius undecimradiatus

Devario fangfangae Danio aff. strigillifer

Doryichthys contiguus Doryichthys deokhatoides

Garra theunensis Garra cf. pingi

Glyptothorax aff. fuscus 1 Glyptothotrax lampris

Glyptothorax horai Glyptothorax macromaculatus

Hemimyzon papilio Hemimyzon sp. n. aff. elongata

Hypsibarbus vernayi Barbodes daruphani

Labeo pierrei Labeo yunnanensis

Laides longibarbis Laides hexanema

Laubuka laubuca Chela laubuca

Mastacembelus armatus Mastacembelus armatus and M. favus

Micronema apogon Kryptopterus apogon

Micronema cheveyi Kryptopterus cheveyi

Monopterus javanensis Monopterus albus

Nemacheilus arenicolus Nemacheilus sp. n. aff. pallidus

Neodontobutis aurarmus Odontobutis aurarmus

Neolissochilus blanci Neolissochilus stracheyi

Onychostoma fusiforme Onychostoma cf. elongata

Onychostoma meridionale Onychostoma sp. n. cf. elongata

Opsarius koratensis Barilius koratensis

Opsarius pulchellus Barilius pulchellus

Oreoglanis lepturus Oreoglanis delacouri (in part)

Oreoglanis hypsiurus Oreoglanis delacouri (in part)

Oryzias pectoralis Oryzias sinensis (in part)

Oryzias sp. 'river' Oryzias sinensis (in part)

Oryzias sp. 'swamp' Oryzias sinensis (in part)


Appendix 2. Continued.Annexe 2. Suite.

Present name Earlier name

Osteochilus striatus Osteochilus sp. n. aff. sarawakensis

Osteochilus vittatus Osteochilus hasselti

Pao abei Tetraodon sp. n. yellow spots

Pao suvattii Tetraodon suvattii

Papuligobius ocellatus Rhinogobius ocellatus

Pseudecheneis sympelvica Pseudecheneis sp. n.

Pterocryptis inusitata Pterocryptis cochinchinensis

Rasbora myersi Rasbora dusonensis

Rhinogobius lineatus Rhinogobius mekongianus

Rhodeus laoensis Rhodeus sp. n. aff. spinalis

Scaphognathops theunensis Scaphognathops sp. n. red caudal

Schistura atra Schistura sp. n. black

Schistura dorsizona Schistura sp. n. saddles

Schistura isostigma Schistura geisleri

Schistura kongphengi Schistura cf. kengtungensis

Schistura nudidorsum Schistura sp. n. naked back

Schistura obeini Schistura sp. n. red tail

Schistura punctifasciata Schistura sp. n. narrow bars

Schistura sombooni Schistura aff. breviceps

Schistura tubulinaris Schistura sp. n. tubular naris

Serpenticobitis zonata new genus new species

Sundasalanx mekongensis Sundasalanx aff. microps

Syncrossus beauforti Botia beauforti

Syncrossus helodes Botia helodes

Terateleotris aspro Odontobutis sp. n.

Tor laterivittatus Tor sp. n. red fins

Toxotes microlepis Toxotes chatareus

Trichopodus trichopterus Trichogaster trichopterus

Xenentodon canciloides Xenentodon sp. n. large scales

Yasuhikotakia caudipunctata Botia caudipunctata

Yasuhikotakia eos Botia eos

Yasuhikotakia lecontei Botia lecontei

Yasuhikotakia modesta Botia modesta

Yasuhikotakia longidorsalis Botia longidorsalis

the fishes of the nam theun and xe bangfai drainages, laos...the diversity of inland fishes in...

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