BioSystems 90 (2007) 188–196

The use of fish community structure as a measure of ecologicaldegradation: A case study in two tropical rivers of India

S.K. Das a,∗, D. Chakrabarty b

a Environmental Science Department, Netaji Subhas Open University, 1 Wood Burn Park, Kolkata 700020, Indiab Department of Zoology, Krishnagar Government College, Krishnagar 741101, Nadia, West Bengal, India

Received 3 August 2006; accepted 16 August 2006

Abstract

Fish community structure and water chemistry of two tropical rivers of West Bengal, an eastern province of India, were studied

for two annual cycles (January 2003–December2004) and a higher degree of pollution was found in one river (the Churni) than in theother river (the Jalangi). This was reflected in the water quality as well as in fish community structure of the rivers. We observed that63.6% of fish species appeared to have been eliminated from the polluted Churni river since 1983 in 20 years. For the protection offish biodiversity and enhancement of fish production, a rational management program should be implemented for the Churni river.© 2006 Elsevier Ireland Ltd. All rights reserved.

Degrad

Keywords: River pollution; Fish community structure; Trophic level;

1. Introduction

The responses of particular communities, especiallyfish, within aquatic ecosystems reflect the amount ofdegradation of that system (Wichert and Rapport, 1998).Fish diversity was shown to be a good indicator of envi-ronmental stress (Barella and Petere, 2003) in rivers.The Churni and Jalangi rivers, situated in District Nadia,of West Bengal, an eastern province of India (Fig. 1)are a present interest of study regarding the fish com-munity study. The Jalangi river is situated approximate25 km away in north from the Churni river, both riversare situated within the same climatic area and had sim-

ilar fish fauna 22 years ago (Chakrabarty, 1983). Overthe past 15–20 years, the Churni river has suffered aloss in fish species as a result of water pollution and

∗ Corresponding author at: Department of Zoology, Krishnagar Gov-ernment College, Krishnagar 741101, Nadia, West Bengal, India.Tel.: +91 03472 256074.

E-mail address: das sanjibm@yahoo.com (S.K. Das).

0303-2647/$ – see front matter © 2006 Elsevier Ireland Ltd. All rights reservdoi:10.1016/j.biosystems.2006.08.003

ation; Habitat orientation; Similarity index

ecological degradation (Ghosh and Konar, 1991). Bothrivers are branches of the Padma river and ultimatelydischarge into the river Ganga (Fig. 1). These two riversmay be described as twin branch rivers of the Padmariver. The amounts of annual precipitation and annualdischarge of both rivers area almost similar (IWMED,2002).

Among the rivers of West Bengal, the Churni andJalangi are significant, as they are the major source ofsurface water, an income source for thousands of fisher-men and provide fish as food to 0.3 million people nearbyto the adjacent small cities of Ranaghat and Krishna-gar. The objective of this paper is to describe of the fishfauna of two rivers, whose environmental conditions areaffected by anthropogenic activities.

2. Materials and methods

2.1. Study area

The Churni river is a tributary of the Padma river inBangladesh. The Churni river originates in Bangladesh and

ed.

S.K. Das, D. Chakrabarty / BioSystems 90 (2007) 188–196 189

phical

flduttbioRTattC

tlaabSpbs

Fig. 1. Sketch showing the geogra

ows about 95 km in Indian soil. The river is subjected toifferent anthropogenic activities throughout its course. Thepper stretches receive discharges of sugar mill effluents fromhe Darshana sugar mill factory (situated in Bangladesh) andhe lower stretch in India is subjected to water obstruction byamboo-made barrages at several places and it also receivesndustrial effluents and city sewage. The catchments areaf this river includes a medium populated (0.140 million)anaghat municipality (latitude 23.11N, longitude 88.37E).he opposite bank of this river comprises village residentialreas and unorganized small-scale industries, which releaseheir untreated effluents (approximately 24,000 l d−1) intohe river. The river discharges into the Ganges river nearhakdaha.

The Jalangi river flowing from the western boundary of Dis-rict Nadia enters into the city of Krishnagar (latitude 23.24N,ongitude 88.30E, population of about 0.145 million). Flowinglmost straight westwards, it discharges into the Ganges rivert Nabadwip township (IWMED, 2002). There are no such

ig industries in the Municipality area except the Krishnagartate Dairy, which discharges approximately 18,000 l d−1 ofrocessed water in to the river. People residing near the easternank of the river use the water for bathing purposes within thetudy area.

location of the two rivers studied.

2.2. Water quality

An approximate stretch of 15 km of both the Churni andJalangi rivers had been selected for sampling in order to focusthe pollution impact on the township of Ranaghat and Krish-nagar cities. All the industrial units are located within this areafor both the river. Three sampling zones at approximately 5 kmapart were selected at upstream, midstream and down stream ofeach river as identified in Fig. 1. Each zone consisted of threesampling sites, nearby two opposite banks and in midstreamand has been demarcated as east (E), next to the township, andmiddle (M) and west (W) opposite to the township. Results areexpressed as the mean of the three sites for a zone.

Water samples were collected monthly between 9 and11 a.m. from lotic zones at a depth of 5 cm from the surface,in 2 l plastic containers for physico-chemical analysis and alsocollected in sterilized glass tubes for bacteriological analysisin the laboratory following Standard Methods (2002).

Temperature and pH were measured immediately after

collection of the sample. Physico-chemical analysis for con-ductivity, dissolved oxygen (DO), initial biological oxygendemand (BOD), total dissolved solids (TDS), total alkalinity,total hardness, phosphorus, total nitrogen were performed inthe laboratory on the same day or within a week. Analyses of

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190 S.K. Das, D. Chakrabarty

all parameters were done following the standard methods asoutlined in Standard Methods (2002) and in Wetzel and Likens(2004).

2.3. Collection of fish community data

Fish catches at weekly intervals were identified to speciesat each sampling site in each river using a pre-tested structuredinterview schedule with local fishermen from fish landing sta-tions up to 70 km for both rivers. The fish capturing sites wereadjacent to our sampling zones. Fish were identified when col-lected by local fishermen. The nets used for fishing were gill ordrag net with floaters and sinkers. The gill nets used were 200 min length and 12 m in width. The net easily reached bottom ofthe rivers studied and covered the length between two banks.The fishing efforts were almost same in all the sampling zones.A number of representative fish caught by the fishermen werefixed in formalin and transported to the laboratory for study. Aset of indicators, i.e., weight, habitat orientation, trophic struc-ture were examined.

2.4. Definition of trophic structure and score

Various members of a fish community are classified intotrophic groups based on feeding habits (Karr et al., 1986;OPEA, 1987). Analyzing the gut content we found four typesof “trophic level” fishes (planktivore = PL, benthic feeder = BE,omnivore = OM, carnivore = CA) in both of the rivers (Table 3).The trophic level score (Wichert and Rapport, 1998; Gauch,1982) denotes the relative frequency of the fish using the par-ticular trophic level among all the trophic level available in thataquatic system. For example, there are four species of plank-tivorous fish in the Churni river out of a total of 16 species. Thescore is thus 100 × (4/16) or 25 (Table 2).

2.5. Define of habitat orientation and score

Fish were classified into three general groups with respectto habitat orientation: pelagic (P), generalist (G) and benthic(B) (Jhingran, 1997). Habitat orientation score (Wichert andRapport, 1998; Gauch, 1982) denotes the relative frequencyof the fish using the particular habitat among all the habitatsavailable in that aquatic system. For example, there are sixspecies of pelagic fish in the Churni river out of a total of16 species. The score is thus 100 × (6/16) or 37.5 (Table 2).The mean score of habitat orientation (Table 2) was comparedbetween the two rivers.

2.6. Similarity and dissimilarity indices to identifyindicator species

Sorensen’s coefficient (SC) developed an index called the

similarity index, which measures similarity between two habi-tats (habitats A and B).

SC = 2a

2a + b + c

stems 90 (2007) 188–196

where a = number of species common to two habitats,b = number of species present in habitat B but absent in habi-tat A, c = number of species present in site A but absent insite B. The index value varies between 0 and 1. Zero indicatesno similarity and 1 indicates maximum similarity. CalculatedSorensen’s coefficients (SC) for the fish resources were cal-culated between the two rivers to identify the likely indicatorspecies for pollution (Gauch, 1982; Benson and Magnuson,1992; Odum and Barett, 2005).

An additional composition attribute was Bray-Curtis dis-similarity (BCD), a coefficient shown to be a robust andecologically interpretable index of changes in species com-position (Faith et al., 1987; Legendre and Legendre, 1998).BCD was calculated using the (n = 44) taxa abundance data(standardized using log10(X + 1) transformation; Legendre andLegendre, 1998).

The Bray-Curtis measure (B) is a measure of dissimilarity;hence 1 − B is taken as a measure of similarity:

B =∑ |Xij − Xjk|∑ |Xij + Xjk| , which is on a 0 to 1 scale

where Xij = number of individuals of ith species in sample orhabitat or community j and Xik = number of individuals of ithspecies in sample or habitat or community k.

3. Results

3.1. Water quality

The result of the physico-chemical and biologicalparameters in the Churni and Jalangi rivers showsthe dissolved oxygen content in Churni river waterremained around 5 mg l−1 through most of the year(November–May). During the October monsoon season,the organic matter present in the surface runoff reducedthe level to 3 mg l−1 (Tables 1a and 1b) which is likelyat or near the effective concentration for aquatic life(Jhingran, 1997). This DO sag indicated the continuouspresence of substantial amount of dissolved organic loadin the water. In contrast, the Jalangi river water remainedsupersaturated with respect to dissolved oxygen throughmost of the time of the year (Tables 1a and 1b).Slight reductions in oxygen concentration were observedduring monsoon (June–August) months. The averagelevel of BOD was high in case of the Churni river(Tables 1a and 1b) and the mode of seasonal varia-tion in these two rivers were to some extent similar(Tables 1a and 1b). Both rivers were affected by theoccasional addition of degraded or partially degraded

organic substances from the banks through erosion. Themean level of hardness of the Churni river was higherthan the Jalangi during the study period and showed asimilar trend in seasonal variation (Tables 1a and 1b).

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Table 1aMean monthly variation of grand average values of some physico-chemical characteristics from different zones comprising three sites on the Churni riverParameter Months

January February March April May June July August September October November December

Temperature (◦C) 20 ± 0.51 22 ± 0.54 25 ± 0.53 29 ± 0.69 30 ± 0.56 29 ± 0.65 28 ± 0.55 28 ± 0.59 29 ± 0.67 29 ± 0.74 26 ± 0.68 24 ± 0.77pH 8.14 ± 0.16 8.40 ± 0.19 8.32 ± 0.14 8.15 ± 0.20 8.32 ± 0.16 8.30 ± 0.18 8.10 ± 0.20 8.09 ± 0.15 8.31 ± 0.18 8.42 ± 0.14 8.00 ± 0.16 8.12 ± 0.19Conductivity (�S cm−1) 595.4 ± 15.6 581.8 ± 18.6 651.8 ± 16.2 702 ± 11.3 640.6 ± 17.5 410.2 ± 10.1 520.0 ± 15.4 510.3 ± 13.7 419.9 ± 15.6 279.8 ± 19.2 467.8 ± 20.5 503.6 ± 18.3Total solids (mg l−1) 493.3 ± 18.6 540.0 ± 15.3 508.8 ± 17.8 582.2 ± 20.8 503.3 ± 23.9 247.7 ± 19.4 365.3 ± 24.8 335.3 ± 18.9 320.9 ± 16.7 274.1 ± 20.4 443.3 ± 23.7 495.5 ± 19.9Total alkalinity (mg l−1) 390.4 ± 17.3 410.0 ± 15.8 437.6 ± 18.6 370.2 ± 20.3 377.8 ± 16.5 290.0 ± 19.9 347.2 ± 15.4 283.3 ± 17.8 223.9 ± 19.5 196.5 ± 20.8 423.3 ± 16.9 353.2 ± 18.5Total hardness (mg l−1) 229.2 ± 15.8 319.6 ± 18.3 234.4 ± 16.5 273.7 ± 19.6 196.7 ± 17.9 147.7 ± 20.8 177.0 ± 16.7 173.3 ± 19.4 166.8 ± 15.2 156.6 ± 17.5 281.3 ± 19.8 232.4 ± 16.3Dissolved oxygen (mg l−1) 4.80 ± 0.65 4.70 ± 0.67 4.78 ± 0.71 4.76 ± 0.69 4.77 ± 0.68 4.50 ± 0.66 4.30 ± 0.76 4.02 ± 0.69 3.00 ± 0.77 3.10 ± 0.80 4.90 ± 0.67 4.85 ± 0.76Biological oxygen demand

(mg l−1)3.24 ± 0.43 2.66 ± 0.65 3.18 ± 0.59 2.35 ± 0.74 2.99 ± 0.68 3.51 ± 0.79 2.53 ± 0.49 2.73 ± 0.66 2.86 ± 0.67 2.93 ± 0.55 4.80 ± 0.48 2.93 ± 0.77

Total nitrogen (mg l−1) 4.04 ± 0.08 3.89 ± 0.06 4.53 ± 0.09 5.70 ± 0.07 5.55 ± 0.06 4.36 ± 0.05 3.61 ± 0.08 3.49 ± 0.09 3.31 ± 0.10 4.39 ± 0.08 4.43 ± 0.06 4.18 ± 0.07Total phosphorus (mg l−1) 1.83 ± 0.09 1.61 ± 0.10 1.20 ± 0.08 2.02 ± 0.11 2.40 ± 0.13 3.39 ± 0.10 3.45 ± 0.09 3.53 ± 0.12 3.40 ± 0.14 2.02 ± 0.89 1.82 ± 0.13 1.55 ± 0.14Total coliform (MPN dl−1) 0.73 1.18 1.35 4.63 1.12 3.45 9.88 7.39 5.53 4.76 1.65 1.79

Table 1bMean monthly variation of grand average values of some physico-chemical characteristics from different zones comprising three sites on the Jalangi riverParameter Months

January February March April May June July August September October November December

Temperature (◦C) 19 ± 0.55 24 ± 0.65 28 ± 0.63 29 ± 0.58 31 ± 0.76 28 ± 0.65 28 ± 0.64 28 ± 0.69 27 ± 0.62 27 ± 0.65 25 ± 0.79 21 ± 0.69pH 7.70 ± 0.19 7.68 ± 0.14 7.74 ± 0.17 7.80 ± 0.20 7.92 ± 0.15 7.59 ± 0.18 7.55 ± 0.14 7.39 ± 0.20 7.65 ± 0.15 7.97 ± 0.17 7.87 ± 0.14 7.75 ± 0.20Conductivity

(�S cm−1)492.8 ± 15.3 505.1 ± 13.7 585.7 ± 11.6 535.3 ± 17.5 416.8 ± 12.4 332.0 ± 19.5 220.1 ± 14.6 205.5 ± 20.1 199.0 ± 10.6 191.0 ± 15.8 429.6 ± 18.8 445.9 ± 14.5

Total solids(mg l−1)

437.7 ± 16.3 473.3 ± 15.8 502.2 ± 19.3 471.1 ± 22.6 217.7 ± 15.9 251.1 ± 21.4 338.8 ± 18.7 256.8 ± 16.8 273.6 ± 23.4 250.0 ± 18.9 448.8 ± 24.3 384.4 ± 19.5

Total alkalinity(mg l−1)

382.2 ± 16.8 395.8 ± 18.3 332.1 ± 15.9 265.8 ± 17.6 326.2 ± 20.4 218.0 ± 15.6 117.1 ± 19.9 125.6 ± 16.4 129.3 ± 18.7 133.0 ± 15.1 357.1 ± 20.7 300.1 ± 16.5

Total hardness(mg l−1)

206.7 ± 19.3 296.5 ± 15.8 197.1 ± 17.9 182.6 ± 19.5 150.2 ± 15.9 133.0 ± 20.5 170.8 ± 16.4 172.3 ± 18.6 174.5 ± 15.7 175.0 ± 17.2 291.3 ± 20.1 288.0 ± 18.4

Dissolved oxygen(mg l−1)

10.3 ± 0.61 10.0 ± 0.68 8.70 ± 0.74 8.80 ± 0.60 9.00 ± 0.73 6.60 ± 0.67 6.80 ± 0.79 7.40 ± 0.65 8.00 ± 0.68 8.20 ± 0.76 9.00 ± 0.66 9.98 ± 0.63

Biological oxygendemand (mg l−1)

1.70 ± 0.55 1.50 ± 0.65 1.30 ± 0.48 1.90 ± 0.68 2.00 ± 0.44 1.40 ± 0.76 1.50 ± 0.53 1.79 ± 0.68 1.95 ± 0.80 2.00 ± 0.49 1.90 ± 0.63 1.20 ± 0.76

Total nitrogen(mg l−1)

2.03 ± 0.05 1.50 ± 0.08 1.30 ± 0.06 1.90 ± 0.09 2.00 ± 0.07 1.40 ± 0.05 1.50 ± 0.06 1.79 ± 0.10 1.95 ± 0.08 2.00 ± 0.07 1.90 ± 0.05 1.20 ± 0.09

Total phosphorus(mg l−1)

0.63 ± 0.89 0.60 ± 0.11 0.43 ± 0.10 0.85 ± 0.13 1.01 ± 0.09 1.39 ± 0.11 1.28 ± 0.14 1.29 ± 0.10 1.35 ± 0.13 1.02 ± 0.12 0.85 ± 0.10 0.78 ± 0.09

Total coliform(MPN dl−1)

0.69 1.07 0.41 0.55 0.87 2.10 1.19 1.05 0.93 0.63 1.63 1.10

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The variation in total alkalinity showed a trend simi-lar to that of hardness (Tables 1a and 1b). The valuesof total solids were almost similar in the two rivers.The Churni river water experienced its peak in con-ductivity values in April and the Jalangi had its peakvalue in March. However, no definite seasonal trend wasfound in the two rivers regarding its conductivity val-ues (Tables 1a and 1b). The highest differences wereobserved through July–November in the whole studyperiod between the two rivers. The level of total nitrogenand total phosphorus in the Jalangi was considerably lessthan in the Churni (Tables 1a and 1b). Performing t-tests,significant differences (P < 0.001) were found in the con-centration of DO, BOD, total-P, total-N, total alkalinityand conductivity throughout the year between the rivers.Significant differences (P < 0.001) were also found intotal coliform count from March to October between thetwo rivers studied. This study revealed that the Churniriver was more contaminated with bacteria (MPN) thanthe water of the Jalangi river (Tables 1a and 1b). Thiswas possibly because of untreated sewage disposal tothe river Churni.

3.2. Fish community indices

The data for fish availability in 1983 indicate simi-lar fish communities in both rivers, each represented by44 different types of fish. While the Jalangi today stillcontains 44 fish types, only 16 are found today in theChurni.

The mean score for habitat orientation (37.19 forJalangi and 34.37 for Churni) showed no differencesbetween the two rivers (Table 2) but the mean trophiclevel score for the fish of the river Churni (34.37) was24.6% higher than that for the river Jalangi (27.57). At-test for trophic level score for common fishes betweenthe rivers showed significant difference (P < 0.001). Thisindicates that the fishes of the river Churni were likelyresponding to ecosystems stress, resulting in the degra-dation of community structure compared to the Jalangiriver. However, the biodiversity of the fishes, present inthe two rivers was markedly different as the Churni has15.38 times fewer fish species than the Jalangi. Fish pro-duction was also reduced, and was 42.31 times less inthe Churni than in the Jalangi (Table 2).

The data for similarity index (Sorensen’s coefficient)showed its least value (0.266) and the dissimilarity index(Bray-Curtis) showed its maximum value (0.733) for car-

nivorous species (Table 3) among four types of ‘trophiclevel’ fishes. The Bray-Curtis index, for trophic levelidentified the carnivore for species (>0.733) (Table 3) asan indicator species for pollution.

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4. Discussion

In general, the dissolved organic load is a likely causefor concern in the Churni river, which regularly receivesuntreated municipal and industrial sewage. The excessphosphorus may trigger proliferation of nitrogen-fixingalgae, thereby enhancing the state of eutrophication andloss of biodiversity.

Comparing the biodiversity of fishes in the two riverswe found 16 common fishes in both rivers and other 28fishes are missing from the Churni. The observation thatthese fish have disappeared in the Churni since 1983, inaddition to the greater organic pollution measured in theChurni, serve as evidence that this river may be affectedby pollution and other anthropogenic activity. Amongthe fish taxa living in the Churni, six (serial numbers: 1,2, 3, 4, 15 and 16 (Table 2)) are cultivatable species of fishin that nearby locality. The maximum age of the fish cap-tured from the Churni is less than 1 year of age (Table 2)as calculated from their weight and size (Jhingran, 1997)in almost all the cases, and indicates that the river has lostall its inherent fishes due to pollution. The fish collectedare accidentally entrained in the river system during therainy season, when nearby ponds are flooded and theconnection established through canals. The remaining10 fish types (Table 2) are not cultivatable species in thatarea, although they are resistant to pollution. Perform-ing the analysis for similarity index for trophic level wefound the carnivore species group (Table 3) has a scoreclose to 0 (>0.266) and can be used as an indicator taxonfor pollution (Table 3).

The mean trophic level score for the fish of the Churniwas 24.6% higher than that for the Jalangi. This indi-cates that the fishes of the Churni were likely respondingto ecosystems stress (Rapport, 1995), resulting in thedegradation of community structure compared to theJalangi river. In contrast, high diversity of fish speciesin the Jalangi river represents a variety of suitable habi-tat and food types to support many different species, asdescribed by Washington (1984). The habitat orientationscore did not appear to be a useful indicator of ecosys-tem stress. It is in agreement with Wichert and Rapport(1998) as habitat orientation score is not an indicator forecosystem stress in lotic system.

From the study of trophic level of fishes it appears thatomnivores are often the most tolerant of degradation orecosystem dysfunction because they are able to consumefood from a wide variety of sources in a changing ecosys-

tem (Wichert and Rapport, 1998). Other trophic levels,in order of sensitivity to degradation, beginning withthe least sensitive, include: planktivores, insectivores,benthic insectivores (e.g., benthic feeders) and insec-

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Table 2Systemic position, community indices and production of fish in two annual cycles (January 2003–December 2004) in the two rivers studied

Systemicposition

Trophic levelnature

Trophic level score Habitatorientation nature

Habitatorientation score

Maximum sizecaptured (kg)

Mean annual fish productionin 1000 kg ha−1 year−1

RC RJ RC RJ RC RJ RC RJ

Order: Cypriniformes, family: Cyprinidae, subfamily: Cyprininae1. Catla catla

(Hamilton-Buchanan)aPL 25.00 31.81 P 37.50 45.45 0.300 7.000 0.6 ± 0.06 14 ± 1.1

2. Labeo rohita(Hamilton-Buchanan)a

PL 25.00 31.81 G 37.50 36.36 0.200 5.800 0.4 ± 0.020 11.6 ± 1.14

3. Labeo bata (Hamilton) PL Eliminated 31.81 G Eliminated 36.36 Eliminated 0.200 Eliminated 0.4 ± 0.034. Labeo calbasu (Hamilton)a BE 12.50 11.36 B 25.00 18.18 0.200 4.600 0.4 ± 0.018 9.2 ± 0.825. Cirrhinus mrigala

(Hamilton-Buchanan)aBE 12.50 11.36 B 25.00 18.18 0.300 4.000 0.6 ± 0.020 8 ± 0.7

6. Puntius sarana sarana(Hamilton-Buchanan)a

PL 25.00 31.81 P 37.50 45.45 0.005 0.020 0.01 ± 0.0014 0.04 ± 0.0038

7. Puntius sophore(Hamilton-Buchanan)

PL Eliminated 31.81 P Eliminated 45.45 Eliminated 0.020 Eliminated 0.04 ± 0.0035

8. Puntius ticto(Hamilton-Buchanan)a

PL 25.00 31.81 P 37.50 45.45 0.025 0.010 0.05 ± 0.012 0.02 ± 0.0028

Order: Cypriniformes, family: Cyprinidae, subfamily: Cultrinae9. Chela laubuca

(Hamilton-Buchanan)aOM 50.00 27.27 P 37.50 45.45 0.025 0.030 0.05 ± 0.013 0.06 ± 0.0054

Order: Cypriniformes, family: Cyprinidae, subfamily: Rasborinae10. Amblypharyngodon mola

(Hamilton-Buchanan)PL Eliminated 31.81 P Eliminated 45.45 Eliminated 0.010 Eliminated 0.02 ± 0.0018

11. Esomus danricus(Hamilton-Buchanan)

PL Eliminated 31.81 P Eliminated 45.45 Eliminated 0.010 Eliminated 0.02 ± 0.0016

12. Mystus aor (Hamilton) OM Eliminated 27.27 G Eliminated 36.36 Eliminated 1.500 Eliminated 3 ± 0.2913. Mystus seenghala (Skyes)a OM 50.00 27.27 G 37.50 36.36 0.020 0.030 0.04 ± 0.015 0.06 ± 0.005814. Mystus vittatus horai

(Jayram)aOM 50.00 27.27 G 37.50 36.36 0.025 0.030 0.05 ± 0.015 0.06 ± 0.0056

15. Mystus bleekari (Day) OM Eliminated 27.27 G Eliminated 36.36 Eliminated 0.030 Eliminated 0.06 ± 0.005816. Rita rita (Hamilton) OM Eliminated 27.27 B Eliminated 18.18 Eliminated 3.000 Eliminated 6 ± 0.59

Order: Cypriniformes, family: Siluridae17. Ompok pabo

(Hamilton-Day)CA Eliminated 29.54 G Eliminated 36.36 Eliminated 0.030 Eliminated 0.06 ± 0.0058

18. Wallago attu (Schneider) CA Eliminated 29.54 G Eliminated 36.36 Eliminated 18.000 Eliminated 36 ± 1.6

Order: Cypriniformes, family: Schilbeidae19. Ailia coila (Hamilton) PL Eliminated 31.81 P Eliminated 45.45 Eliminated 0.200 Eliminated 0.4 ± 0.0420. Eritropiichlhy gongwaree

(Skyes)CA Eliminated 29.54 P Eliminated 45.45 Eliminated 0.200 Eliminated 0.4 ± 0.04

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Table 2 (Continued)

Systemicposition

Trophic levelnature

Trophic level score Habitatorientation nature

Habitatorientation score

Maximum sizecaptured (kg)

Mean annual fish productionin 1000 kg ha−1 year−1

RC RJ RC RJ RC RJ RC RJ

21. Eutropifchthys vacha(Hamilton)

CA Eliminated 29.54 P Eliminated 45.45 Eliminated 0.200 Eliminated 0.4 ± 0.038

Order: Cypriniformes, family: Clariidae22. Clarias batrachus

(Linnaeus)aOM 50.00 27.27 P 37.50 45.45 0.050 0.300 0.1 ± 0.018 0.6 ± 0.057

Order: Cypriniformes, family: Heteropneustidae23. Heteropneustes fossilis

(Bloch)aOM 50.00 27.27 P 37.50 45.45 0.100 0.300 0.2 ± 0.020 0.6 ± 0.054

Order: Perciformes, family: Gobiidae24. Glossogobius guiris

(Hamilton-Buchanan)aOM 50.00 27.27 B 25.00 18.18 0.010 0.450 0.02 ± 0.018 0.9 ± 0.081

25. Gobias striatuis (Day)a OM 50.00 27.27 B 25.00 18.18 0.020 0.050 0.04 ± 0.015 0.1 ± 0.011

Order: Perciformes, family: Anabantidae26. Anabas testudineus

(Bloch)aOM 50.00 27.27 G 37.50 36.36 0.020 0.075 0.04 ± 0.015 0.15 ± 0.014

Order: Perciformes, family: Belontiidae27. Trichogaster fasciatus

(Bloch)OM Eliminated 27.27 P Eliminated 45.45 Eliminated 0.015 Eliminated 0.03 ± 0.0029

28. Nandus nandus (Bloch) CA Eliminated 29.54 G Eliminated 36.36 Eliminated 0.030 Eliminated 0.06 ± 0.0053

Order: Perciformes, family: Channidae29. Channa striatus (Bloch)a CA 12.50 29.54 G 37.50 36.36 0.015 2.500 0.03 ± 0.020 5 ± 0.05230. Channa punctata (Bloch)a CA 12.50 29.54 G 37.50 36.36 0.050 0.400 0.1 ± 0.015 0.8 ± 0.07831. Channa gachua (Bloch) CA Eliminated 29.54 G Eliminated 36.36 Eliminated 0.400 Eliminated 0.8 ± 0.07632. Channa marulius (Bloch) CA Eliminated 29.54 G Eliminated 36.36 Eliminated 0.500 Eliminated 1 ± 0.1533. Channa orientalis (Bloch) CA Eliminated 29.54 G Eliminated 36.36 Eliminated 0.400 Eliminated 0.8 ± 0.075

Order: Perciformes, family: Mastacembelidae34. Mastacembelus

bengalensis(Hamilton-Buchanan)

BE Eliminated 11.36 B Eliminated 18.18 Eliminated 0.150 Eliminated 0.3 ± 0.028

35. Macrognathus pancalus(Hamilton-Buchanan)

BE Eliminated 11.36 B Eliminated 18.18 Eliminated 0.150 Eliminated 0.3 ± 0.024

Order: Perciformes, family: Synbranchidae36. Amphipnous cuchia

(Hamilton-Buchanan)BE Eliminated 11.36 B Eliminated 18.18 Eliminated 1.000 Eliminated 2 ± 0.21

Order: Osteoglossiformes, family: Notopteridae37. Notopterus notopterus

(Pallas)CA Eliminated 29.54 P Eliminated 45.45 Eliminated 0.400 Eliminated 0.8 ± 0.068

38. Notopterus chitala (Pallas) CA Eliminated 29.54 P Eliminated 45.45 Eliminated 5.000 Eliminated 10 ± 1.1

S.K.D

as,D.C

hakrabarty/B

ioSystems

90(2007)

188–196195

Order: Osteoglossiformes, family: Ambassidae39. Chanda nama

(Hamilton-Buchanan)CA Eliminated 29.54 P Eliminated 45.45 Eliminated 0.010 Eliminated 0.02 ± 0.002

Order: Clupiformes, family: Clupeidae40. Hilsa illsha (Hamilton) PL Eliminated 31.81 G Eliminated 36.36 Eliminated 0.600 Eliminated 1.2 ± 0.1341. Gadusia chapra

(Hamilton)PL Eliminated 31.81 P Eliminated 45.45 Eliminated 0.050 Eliminated 0.1 ± 0.018

Order: Clupiformes, family: Engraulidae42. Setipinna phasa (Hamilton) PL Eliminated 31.81 P Eliminated 45.45 Eliminated 0.010 Eliminated 0.02 ± 0.0021

Order: Mugiliformes, family: Mugilidae43. Mugil korsula (Forsskal) PL Eliminated 31.81 P Eliminated 45.45 Eliminated 0.020 Eliminated 0.04 ± 0.0036

Order: Beloniformes, family: Belonidae44. Xenentodon cancila

(Hamilton)PL Eliminated 31.81 P Eliminated 45.45 Eliminated 0.020 Eliminated 0.04 ± 0.0038

Mean score 34.37 27.57 34.37 37.19Standard deviation 16.23 6.06 5.41 11.97Coefficient of variation 47.22 21.98 15.74 34.48

RC = river Churni; RJ = river Jalangi.a Common fishes in both the river.

Table 3Data regarding trophic level, habitat orientation, similarity index and dissimilarity index

Ecological characteristics study Trophic level analysis Habitat orientation analysis

RC RJ RC RJ

Total occurrence of particular types of fishes PL = 04, BE = 02, OM = 08, CA = 02 PL = 14, BE = 05, OM = 12, CA = 13 P = 06, G = 06, B = 04 P = 20, G = 16, B = 08Total 16 44 16 44Similarity index PL = 0.444, BE = 0.571, OM = 0.80, CA = 0.266 P = 0.461, G = 0.545, B = 0.666Dissimilarity index PL = 0.555, BE = 0.428, OM = 0.200, CA = 0.733 P = 0.538, G = 0.454, B = 0.333

PL = planktivores, BE = benthic feeder, OM = omnivore, CA = carnivore. P = pelagic, G = general, B = benthic. RC = river Churni; RJ = river Jalangi.

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196 S.K. Das, D. Chakrabarty

tivores/piscivores, carnivores at the top of the trophicstructure (Karr and Dudley, 1981). In the least disturbedsystems, a higher proportion of species present wouldbelong to the benthic feeders and carnivores groups thanat heavily degraded sites. As degradation intensifies,those species at the top of the trophic structure, i.e., thecarnivores, would disappear first, followed in sequenceby benthic insectivores, general insectivores, plankti-vores and omnivores (Wichert and Rapport, 1998). Inthe Churni, only 2 carnivore species are found out of13 such species available in the Jalangi. Performing theanalysis for similarity index for trophic level we foundthe carnivore species group can be used as an indicatortaxon for pollution (Table 3). The dissimilarity index,for the carnivore species (Table 3) also supports the ideathat the species can be used as an indicator of pollution.

In conclusion it appears that some structural prop-erties of fish communities in the Churni river changedbetween 1983 and 2003. The changes appear related tovarious anthropogenic activities and industrial practices.Detailed studies are required to quantify the changesto predict a future action plan to check further loss ofaquatic biodiversity. In this study, the habitat orientationscore did not appear to be a useful indicator of ecosys-tem stress. It is in agreement with Rapport (1995) as thehabitat orientation score is not an indicator for ecosystemstress in lotic ecosystems.

Acknowledgements

The authors are grateful to Mr. B. Roy, Assistant Pro-fessor of Statistics, and Krishnagar Government Collegefor his valuable suggestions.

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