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MARICHARRLong-term effects of salinity acclimation methods on growth

and osmoregulation in Arctic charr Salvelinus alpinus

Mismunandi aðferðir við seltuaðlögun bleikju og langtímaáhrif þeirra á vöxt og seltustjórnun

Final activity report: R-058-12

Authors:Tómas Árnason, Hafró

Snorri Gunnarsson, Akvaplan Niva Albert K. Imsland, Akvaplan Niva

Heiðdís Smáradóttir, Íslandsbleikja

1

Abstract

Three groups of Arctic charr Salvelinus alpinus were subjected to three different methods of

salinity acclimation before transfer from low salinities to intermediate and high salinity

regimes (20, 21-26 and 32ppt). Before transfer, one group was reared in slightly brackish

water (3.7 ppt) in indoor tanks under continuous light (group called BW), the second group

was given supersmolt® feed for 38 days in fresh water under continuous light in open outdoor

tanks (group called SF), and the third group was reared under the same conditions as group

SF, except it was not given supersmolt feed (group C). Group BW and SF had the highest gill

NKA activity at transfer to high salinities. In spite of lower gill NKA activity at the time of

transfer, however, group C showed similar long-term growth, survival and

hypoosmoregulatory ability in seawater as group BW and SF when tagged fish of similar

sizes are compared between groups. The uniformity in growth and survival among the

experimental groups was likely due to high gill NKA activity among fish in group C in

February, 62 – 43 days before transfer to higher salinities, and in spite of the reduction in

NKA activity from February to April, there are indications that fish in group C had retained

high salinity tolerance until they were transferred to high salinities in April. Body size was

therefore the determining factor for the SW tolerance of the Arctic charr in the current study.

Based on mortality rates between individuals with different initial sizes, it appears that Arctic

charr of the Hólar strain should be atleast 160 g before they are transferred to seawater (32

ppt).

2

Ágrip

Þrír hópar af bleikju ( BW, SF og C) fengu mismunandi aðlögun fyrir flutning úr lágri seltu í

seiðastöðvum yfir í háa seltu í áframeldisstöðvum. Aðlögun hóps BW fól í sér að fiskurinn

var alinn á seiðastigi í ísöltu vatni (3.7 ppt) undir stöðugri lýsingu. Hópur SF fékk aðlögun

sem fól í sér að fisknum var gefið smolt fóður (Supersmolt®) í 38 daga í ferskvatni undir

berum himni ásamt 24 tíma lýsingu, og hópur C fékk samskonar meðhöndlun á seiðastigi,

nema í stað smoltfóðurs fékk fiskurinn hefðbundið vaxtarfóður. Eftir flutning úr seiðastöð

voru hóparnir aldir við þrjá mismunandi seltuferla (32, 21-26 og 20 ppt) upp í sláturstærð í

þremur eldisstöðvum. Við flutning í eldisstöðvarnar voru hópar BW og SF með hæstu NKA

virknina í tálknum, en þrátt fyrir það var enginn munur á langtíma vexti, lifun og seltustjórn

milli hópa eftir að gögnin voru leiðrétt fyrir mismun í upphafsstærð. Þessi einsleiki milli hópa

stafar líklega af því að hópur C var með háa NKA virkni í febrúar, 62 – 43 dögum áður en

fiskurinn var fluttur í há seltustig, en niðurstöðurnar benda til þess að fiskurinn í hópi C hafi

viðhaldið háu seltuþoli fram að flutning. Seltuþol bleikju í rannsókninni var fyrst og fremst

ákvörðuð af stærð fisksins við flutning í háa seltu. Sé tekið mið af afföllum einstaklinga af

mismunandi stærðum þarf Hólableikja að vera a.m.k. 160 g við flutning í sjó (32 ppt).

3

Contents1. Introduction..................................................................................................................................5

2. Materials and Methods................................................................................................................7

2.1. Experimental fish..................................................................................................................7

2.1.1. Group acclimatized in slightly brackish water (BW).................................................7

2.1.2. Supersmolt group (SF).................................................................................................7

2.1.3. Control group (C).........................................................................................................8

2.2. Seawater challenge tests (SWT)...........................................................................................8

2.3. Experiment 1. Arctic charr reared in seawater....................................................................8

2.4. Experiment 2. Arctic charr reared in 21 – 26ppt...............................................................10

2.5. Experiment 3. Arctic charr reared in 20ppt.......................................................................11

2.6. Parameters studied and sampling.....................................................................................11

2.7. Statistics...............................................................................................................................12

3. Results.........................................................................................................................................13

3.1. Seawater challenge tests.....................................................................................................13

3.2. Experiment 1.......................................................................................................................14

3.2.1. Mortality......................................................................................................................14

3.2.2. Growth.........................................................................................................................16

3.2.3. Condition factor and sexual maturation...................................................................18

3.2.4. Hypo-osmoregulatory ability.....................................................................................19

3.3. Experiment 2.......................................................................................................................20

3.3.1. Mortality and growth.................................................................................................20

3.3.2. Condition factor and sexual maturation...................................................................21


3.4. Experiment 3.......................................................................................................................23

3.4.1. Mortality, growth and feed conversion ratio............................................................23


4. Discussion....................................................................................................................................25

4

1. IntroductionSome populations of wild Arctic charr spend their whole lifecycle in fresh water (FW)

while other move downstream to sea water (SW) where they may stay for a few weeks

before moving back to FW (Flóventsson 1929; Staurnes et al. 1992). Generally, Arctic

charr and other speicies in the Salvelinus genera are relatively large when they develop

the ability to hypoosmoregulate in SW, and the duration of their stay in SW is much

shorter compared to other anadromous salmonid species (McCormick, 2013). However,

the salinity tolerance of Arctic charr varies greatly between FW resident and anadromous

populations (Staurnes et al., 1992; Eliassen et al., 1998), and even among anadromous

populations (Duston et al., 2007; Árnason et al., 2014).

As for most other salmonids, the seawater tolerance of Arctic charr increases during the

spring and early summer and is reduced during late summer or autumn (Jobling et al.

1993; Arnesen et al. 1993b, 1994). The timing of the development of hypo-

osmoregulatory ability and the subsequent movement from FW to SW is driven primarily

by seasonal increase in daylength. Thus, in salmonid aquaculture, artificial seasonal

changes in daylength are commonly administered in order to induce parr-smolt

transformation before transfer into sea-cages. Another method that is used to smoltify

Atlantic salmon involves using specially formulated feed to induce smoltification

(supersmolt®). In Atlantic salmon farming the supersmolt feed eliminates the need for

photoperiod manipulation and ensures that the fish do not de-smoltify, thus allowing

smaller fish to catch up and reach a required size for transfer to SW.

Íslandsbleikja, the largest Arctic charr producer in Iceland, runs two juvenile production

facilities in south-west Iceland, one at Stadur and the other at Öxnalækur. At Stadur, the

juveniles are reared from start-feeding until about 100-150 g in slightly brackish water

(3.7 ppt) under continuous light (LD 24:0), whereas in Öxnalækur they are reared in FW

under continuous light. After the juvenile phase, the on-growing phase takes place in

water of intermediate (16-20 ppt) or high salinities (20-26 ppt).

In a recent study the juveniles from Stadur were found to have high gill NKA activity

and were capable of maintaining osmoregulatory homeostasis and high growth rates in

nearly full strength SW for over a year (Árnason et al., 2014). This finding lead to the

hypothesis that the high on-growing performance in salinity as high as 29 ppt, could to

some extent be attributed to the acclamatory effects of rearing in 3.7 ppt and continuous

light before transfer to high salinities.

5

The aim of this study is to therefore to further examine the short and long-term effects

of rearing Arctic charr juveniles in slightly brackish water prior to exposure to high

salinities. Moreover, we will examine the possible benefits of using the supersmolt®

treatment as a method to induce seawater tolerance in Arctic charr juveniles reared at

Öxnalækur in FW.

6

2. Materials and Methods2.1. Experimental fish

The fish used in this study were the offspring of the 5th generation of pedigreed Arctic

charr from Hólar NW Iceland, which is a crossbreed from an anadromous strain

(Grenlækur S Iceland) and resident freshwater strain (Ölvesvatn NW Iceland). The

alevins were incubated at 6°C in a commercial hatchery in Núpar S Iceland and about one

week before start-feeding alevins were either transferred to a juvenile facility at Stadur in

SW Iceland, or to a similar facility at Öxnalækur in S Iceland. Three large groups of

experimental fish were formed (groups called BW, SF and C, see appendix 1). Unless

otherwise stated, the juveniles at Stadur and Öxnalækur were fed using commercially

formulated feed (Laxá Ltd, Akureyri, Iceland) containing 42-50% crude protein and 21-

26% crude fat. The fish were fed by automatic feeders delivering feed at regular intervals,

24 hours a day.

2.1.1. Group acclimatized in slightly brackish water (BW)

Alevins incubated in February 2012 were transferred to Stadur, where the fish were

reared indoors under continuous light (LD 24:0) in slightly brackish water (BW) which

varied from 3.2 to 4.1ppt (mean = 3.7) due to tidal variation. The rearing temperature was

slowly increased from 6 to 12°C from start feeding until the juveniles reached about 2 g.

Thereafter the temperature was decreased in a stepwise manner until the juveniles were

about 40 g. At this point the temperature had been decreased to about 8°C and was kept

stable until the fish were transferred to higher salinities on 12 March (Experiment 1), or

12 April 2013 (Experiments 2 and 3).

2.1.2. Supersmolt group (SF)

Alevins incubated in February 2012 were transferred to Öxnalækur, where the fish were

reared in FW at 8 – 9°C. The juveniles were reared indoors under continuous light (LD

24:0) until approximately 17 g, and were then transferred to three 50 m3 outdoor tanks in

September 2012. In the outdoor tanks, continuous light was provided by 30 W fluorecent

tubes placed under the footbridge of each tank. On 5 February 2013 when the fish mean

weight was around 90 g the feed was changed from grow out feed to smoltification feed

(SF) (Supersmolt®, 44% crude protein and 24% crude fat). The fish were given smolt-

feed for 38 days, or until they were transferred to higher salinities in experiments 1 – 3 on

14 March 2013.

7

2.1.3. Control group (C)

The fish in group C were hatched in March 2012 and were reared at Öxnalækur under the

same conditions as Group SF, except group C was not given smolt-feed. The fish were

transferred from indoor tanks to outdoor tanks in October 2012 when the fish were

approximately 19 g. The fish were transferred from Öxnalækur to higher salinities in

experiments 1 – 3 on 3 April 2013.

2.2. Seawater challenge tests (SWT)

Gill samples were taken at several occasions from 20 randomly selected fish from each

group during the period when the fish were kept in the juvenile stations. At the same

time, additional 20 juveniles from each group were transferred to the Mariculture

Laboratory of the Marine Research Institute at Stadur where the fish were subjected to 24

h SWT. The fish were transferred in plastic bags to the laboratory with about 1/3 water

(FW or 3.7ppt) and 2/3 oxygen. The transportation of groups B and C took about 1h, but

only several minutes for group BW. In order to adjust for the differences in transport

related stress, the fish from group BW were kept in bags for 1h before the SWT were

initiated. Blood was sampled from each individual 24h after they had been directly

transferred to SW. During the SWT, each group was kept in 7°C SW in one 3.2 m3. The

first SWT was carried out on 4 February 2013, one day before group SF started receiving

smolt-feed. The second SWT was done on 25 February 2013, and the third was carried

out, at the time when group SF stopped receiving smolt-feed and were about to be

transferred to higher salinities on 13 March (Fig. 1). Additional SWT was carried out for

group C on 3 April 2013, at the time when the fish were transferred to higher salinities in

experiments 1 – 3.

2.3. Experiment 1. Arctic charr reared in seawater

The experiment was conducted in the Mariculture Laboratory at Stadur. One week before

groups BW and SF were transferred to the laboratory, on 5 March 2013, about 260

juveniles were randomly selected from each group and individually tagged

intraperitoneally with Trovan® passive transponder tags. The fish were allowed to

recover for one week at 3.7ppt in one 5.6 m3 tank at 8°C (group BW) or FW of the same

temperature in one 2 m3 tank (group SF) before the fish were transferred directly to 7°C

SW in the laboratory. In contrast to group BW and SF, the tagging of fish from group C

was carried out after transfer to the laboratory as there was no empty tank available in the

juvenile facility at Öxnalækur. Thus, instead of tagging the fish in FW, the fish in group

C were tagged one day after transfer to 3.7ppt in the laboratory and allowed to recover for

8

one week before the salinity was increased to 32ppt. In order to evaluate the possible

effects of the one week period at 3.7ppt on the hypo-osmoregulatory ability of fish in

group C, gill samples were taken at the end of the one week recovery on 10 April 2013

from 16 randomly selected fish for analyses of NKA activity. These samples showed that

NKA in group C was not up-regulated in the one week period at 3.7ppt (NKA = 1.8 ±

0.16). In group C, 620 fish were tagged and these fish were randomly divided into two

sub groups on 10 April 2013 (Fig. 1). One was directly (d) transferred to SW without

acclimation (hereafter called Cd) while the other was acclimated (Ca) by stepwise increase

in salinity from 3.7 to 32 ppt in six days (i.e., about 7ppt increase every two days).

-5

0

5

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-5 45 95 145 195 245 295 345 395 445

Salin

ity

//

T

T

T

M1–

S

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S

G

M4BG––

M2

M3BG–

4/4/2013 10/7/2013 9/10/2013 14/1/2014~2/4/2012

– –

~23/4/2012

–

14/5/2013

–

11/6/2013

BG

BG

BG

** * *

BWSFCaCd

Fig. 1. Experimental design in which different methods were used to acclimatize Arctic charr to SW. Group BW was reared at 3.7ppt from start feeding (S) until transferred to SW. Group SF was reared in FW during the juvenile stage and was given smoltification feed for 38 days before transfer to SW (smolt feed period is indicated with dotted red line). Group C was kept in freshwater from start feeding until transferred to 3.7ppt, where they were kept for one week until the salinity was either increased abruptly to SW (Cd), or gradually over the course of one week (Ca). Time of start feeding (S), individual tagging (T), measurements of tagged fish (M), blood samplings (B), gill samplings (G), SWT (*).Samplings and tests which were carried out for all groups at the same time are indicated with black letters, whereas samples taken from one or two groups are indicated with coloured letters.

In the laboratory, each group was reared in two green fibreglass tanks (200×200×70 cm).

All fish were individually weighed under anaesthesia (tricaine methane sulphonate, 0.1 g

L-1, Pharmaq Ltd, UK) on four occasions during the experiment. The initial

measurements (M1, Fig. 1) were carried out on 4 April 2013, i.e. one week before groups

Cd and Ca were transferred to SW, but one month after group BW and SF were exposed to

9

seawater. Growth measurements in experiment 1 are based on tagged fish that survived

from tagging until the termination of the experiment on 14 January 2014.

After the fish had been maintained in SW for about two months (14 May, and 11 June,

Fig. 1), eight fish in each tank were randomly selected and sacrificed in order to take

blood and gill samples. The same procedure was repeated for all groups on 9 October

2013 and 14 January 2014. Condition factor and gonadosomatic index was measured for

each sampled fish, and the same was done for additional 22 fish in each tank at the

termination of the experiment. The sex was determined for all sampled fish and for all

surviving fish at the end of the experiment. Among the surviving fish, the proportion of

males and females was not significantly different in any group (χ2 < 3.84, P>0.05).

In order to adjust for differences in initial body sizes between groups, the growth

trajectories of fish of similar sizes were compared by sorting the tagged individuals

within each group into three size classes (80 – 110 g, 111 – 130 g, 131 – 160 g, and 161 –

180 g). Growth trajectories of fish outside these size classes are not included in this

analyzes, as few fish in group BW and SF were below 80 g and few fish in groups Ca and

Cd were larger than 180 g.

Temperature, oxygen and salinity was measured weekly inside of the tanks. Pure oxygen

was added to the tanks in order to maintain oxygen saturation close to 100% at all times.

The fish were fed to satiation by automatic belt feeders delivering feed constantly, 24 h a

day. The amount placed on the feeders was regulated each day after leftovers from the

day before had been roughly estimated. In each tank the fish were reared under

continuous light provided with two 15 W fluorescent light bulbs (Osram®). Mortality

rates were calculated on a monthly basis as the number dead fish each month as percent

of fish that were alive at the start the month.

2.4. Experiment 2. Arctic charr reared in 21 – 26ppt

Experiment 2 was conducted in six 70 m3 outdoor tanks at Stadur southwest Iceland.

Each group was reared in two tanks. Group SF was the first to be transferred to the

experimental tanks on 14 March 2013. Group C was moved to the tanks 19 days later on

3 April 2013, and group BW was transferred on 11 April 2013. Groups SF and C were

transferred by fish transport vehicle, whereas group BW was pumped from the juvenile

facility at Stadur through a pipe to the outdoor tanks. Approximately 3000 fish were

placed in each tank. One day before the transfer, the mean weights in groups BW, SF and

C were estimated from the combined weight of 100 individuals from each group. The

mean weights at the transfer to the experimental tanks were, 178, 111, and 102 g in

10

groups BW, SF and C respectively. On 23April 2013 the mean body sizes were assessed

by individually weighing 100 fish in each tank. Of these fish, the length of 20 individuals

from each tank was measured for assessment of CF. This procedure was repeated on 27

June and 16 October 2013. At the termination of the experiment, the fish were pumped

from the tanks into a fish transport vehicle and moved to a slaughterhouse in Grindavík.

All fish were weighed individually to the nearest g in a fish processing system (Marel

Ltd. Iceland) after bleeding. At the slaughter house, the sex, maturation status and CF

was assessed from a random sample of 50 fish per tank. As the fish were weighed after

bleeding, the recorded body weights were adjusted by 3% to account for the blood lost

after slaughtering. The fish were starved for one week before slaughter. Group BW was

the first to be slaughtered on 31 January 2014. Group SF was slaughtered on 12 February,

and group C on 6 March 2014.

All groups were reared at 21ppt for the first three months before the salinity was

increased to 26ppt. Thus, the salinity was increased from 21 to 26ppt on 18 June, 7 July

and 15 July 2013 in groups SF, C and BW, respectively. In all tanks there were slight

changes in salinity (about ± 0.6) due to tidal movements. This did not differ between

replicates or salinity groups. In order to reduce seasonal photoperiod effects, the fish were

reared under continuous light provided by four 250 W metal halide light pulps (Philips

Master HPI – T plus) placed on lampposts between the tanks in such a manner that each

tank received approximately the same amount of light. The rearing temperature varied

between 6.5 to 8.3 (mean 7.5 ± 0.05°C) depending on weather, but there were no

significant differences in temperature between tanks (one-way ANOVA, P>0.05).

2.5. Experiment 3. Arctic charr reared in 20ppt

Groups SF, BW and C were transferred from the juvenile stations by a fish transport

vehicle to an on-growing farm at Vatnsleysa on 3 April, 12 April and 14 March

respectively. The experimental groups consisted of 40.240 to 40.675 non-tagged fish and

were each reared in a single 530 m3 tank at 20ppt for the first 6-8 months before

approximately 50% of the fish in each group was moved to a tank of the same size with

the same salinity. Group BW, spent the shortest time in a single tank (6 months) whereas

groups SF and C were kept for 8 months in one tank. The mean temperature in each

group was 5.8, 5.7 and 6°C, for groups BW, SF and C respectively.

2.6. Parameters studied and sampling

Fork length (LF) was measured to the nearest 0.1 cm and body weight to the nearest g.

Condition factor (CF) was calculated as (MLF -3)100, where M is body weight and LF is

11

length. Gonadosomatic index (GSI) was calculated as (GM-1)100, where G is gonad

weight. As there were differences in initial mean weights and time lengths between

measurements among the groups, the thermal growth coefficient (TGC) was used to

calculate growth rates.

TGC=[ ( 3√W t−3√W 0 ) /(T ×t ) ]×1000

Where Wt and W0 are the initial and final mean weights, T is temperature and t the

time in days.

Blood was collected from the caudal vessels using heparinised syringes, centrifuged

at 7000 × g for 6 min, the plasma collected, placed on ice, and stored at -80°C until

analysis. For measurement of branchial NKA activity, the first gill arch at the dorsal side

was cut out and immediately placed in 1.5 ml micro centrifuge vials containing ice-cold

SEI buffer (0.3 mol l-1 sucrose, 20 m mol-1 Na2EDTA, 0.1 mol l-1 imidazole) and stored

in the same way as the plasma samples. Plasma sodium (Na+) was measured by Starlyte

III Electrolyte Analyser (Alfa Wassermann Diagnostics; www.alfawassermannus.com),

and gill NKA activity was analyzed by a standard microassay procedure (McCormick,

1993). All fish were killed by a sharp blow to the head prior to sampling of blood, gills,

gonads and gut.

2.7. Statistics

Significant variation of the sex ratio from 1:1 was determined using chi-square goodness

of fit test. A two-way nested ANOVA with replicates (random) nested within groups

(fixed) was used to test for possible differences in mean body weights, growth rates,

NKA and plasma Na+ between groups. Significant differences in the ANOVA analysis

were followed by Tukey HSD tests. Simple linear regression analyses were done to

examine the relationships between NKA and TGC and between body weight and NKA

among tagged fish. Data are presented as means ± standard error (S.E). All statistical

analysis were done using R version 2.11.2 (the R foundation for statistical computing).

12

3. Results3.1. Seawater challenge tests

There were no mortalities in the 24h SW challenge tests. Group BW had the highest

NKA on 5 February 2013, while no significant difference was found between group SF

and C (Fig 2a, Tukey HSD, P>0.05). Group SF showed significant increase in NKA after

18 days on the smolt-feed treatment (Tukey HSD, P<0.05) and had the highest activity in

25 February and 13 March 2013. Fish in group C showed a significant decrease in NKA

following the first two samplings in February, whereas group BW showed relatively high

and stable NKA throughout. After 24h in SW, there were no significant differences in

plasma Na+ between groups, except on 14 March, when group BW had significantly

higher levels than groups SF and C (Fig 2b Tukey HSD, P<0.05).

0

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05/02/2013 25/02/2013 13/03/2013 05/04/2013

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+-A

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)

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ab b

(a)

(b)

Group SF: Smolt-feeding begins Smolt-feeding seized

Fig. 2. Mean + S.E. (a) gill Na+, K+, ATPase (NKA) activity before, and (b) plasma natrium 24h after transfer to SW. Different lowercase letters indicate statistical difference at the 5% level.

13

In group BW, there were significant positive correlations between body weight and gill

NKA activity in all SW challenge tests (Table 1). In group C, significant relationships

between body weight and NKA were found on 25 February and 13 March but no

significant correlation was found on 5 February and 5 April. No correlations between

body weight and NKA were found in group SF.

Table 1. Simple linear regression analyses between body weight and gill NKA activity in SW challenge tests. Regression coefficient of determination (r2) and slope (a). Asterisks (*) indicate significance of regression slope (P, t-test). **p < 0.01, *p < 0.05, n.s. = non-significant.

SW challenge test BW SF C5.2.2013

r2 0.59 -0.02 -0.04a 0.04 0.01 0.01P ** n.s n.s

25.2.2013r2 0.25 -0.05 0.27a 0.03 0.003 0.06P * n.s *

13.3.2013r2 0.17 -0.04 0.24a 0.02 0.004 0.02P * n.s *

5.4.2013r2 - - 0.04a - - -0.01

P - - n.s

3.2. Experiment 1

3.2.1. Mortality

The overall mortalities in groups BW, SF, Ca and Cd, were 18, 33, 33 and 39%

respectively. The mortality was significantly lower in group BW compared with other

groups, but no significant difference was found between groups SF, Ca and Cd (Chi-

square test, P<0.05). Size analysis reveals that juveniles having small body sizes in April

2013 were the least likely to survive in SW, while large juveniles showed relatively low

mortality rates (Fig. 3.). No significant differences in mortality rates were found between

groups within each size-class in Fig. 3. Feed conversion ratio was similar among all

groups, or 1.34 – 1.39.

14

0

10

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30

40

50

60

70

80 > 80 - 110 111 - 130 131 - 160 161 - 180 > 180

Mor

talit

y (%

)

Size classes (g)

ABCaCdCa

SFBW

Cd

n.s

n.s

n.s n.s

Fig. 3. Overall mortality from 4 April 2013 to 14 January 2014 in Arctic charr with different initial mean weights.

In all groups, the highest mortality rates were observed in the days and weeks following

measurements on 4 April, 10 July and 9 October 2013 (Fig. 3).

Examination of dead fish showed that many of the fish that died in the study had wounds

on various places on their body. Five of these fish were sent to the Institute for

Experimental Pathology for Disease at Keldur, where inoculations from the kidney and

the wounds of the fish were made. The wounds were found to be caused by

Flexi-/Flavobacter-like bacteria, but no known pathogens were found in the kidneys.

0

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Apr-13 May-13 Jun-13 Jul-13 Aug-13 Sep-13 Oct-13 Nov-13 Dec-13 Jan-14

Mor

talit

y (%

mon

th-1

)

BWSFCaCd

Fig. 4. Monthly mortalities from April 2013 to January 2014.

15

In all groups the majority of the fish were smaller than 400 g when they died, or 88, 93,

91 and 95% in groups BW, SF, Ca and Cd respectively, and the mean weights of the dead

fish collected from each group were 202±35, 140±15, 169±15, and 129±12 g

respectively.

3.2.2. Growth

The initial mean weights of fish that survived from start to finish were 166 ± 5, 128 ± 3.4,

106 ± 2.4 and 110 ± 2.9 g in groups BW, SF, Ca and Cd respectively. Growth rates were

generally not significantly different between groups when tagged fish with similar initial

mean weights are compared between groups. However, for the first three months in SW,

fish with initial mean weights from 111-160 g in group Cd had significantly lower growth

than fish with comparable initial weights in groups BW and SF (Tukey HSD, P<0.05,

Fig. 4c and 4d). In the following months, group Cd displayed compensatory growth and

caught up the other groups.

16

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600

800

1000

1200

1400

-20 30 80 130 180 230 280 330

Wei

ght (

g)

0

200

400

600

800

1000

1200

1400

-20 30 80 130 180 230 280 330

Wei

ght (

g)

0

200

400

600

800

1000

1200

1400

-20 30 80 130 180 230 280 330

Wei

ght (

g)––– –

––– – ––– –

––– –

4/4/2013 10/7/2013 9/10/2013 14/1/2014 4/4/2013 10/7/2013 9/10/2013 14/1/2014

4/4/2013 10/7/2013 9/10/2013 14/1/2014 4/4/2013 10/7/2013 9/10/2013 14/1/2014

b c

d e

ns

ns

ns

ns

ns

ns

nsns

ns

ababab

aaabb

ns

ns

ns

ns

ns

abcc

abcc

a

bbb

a

Fig. 5. Growth trajectories of Arctic charr in SW after being subjected to four acclimation treatments. Growth trajectories of all fish (a), growth for fish with initial mean weights ranging from 80 to110 g (b), 111-130 g (c), 131-160 g (d) and 161 -180 g (e). Means sharing the same letter are not significantly different (Tukey HSD, p > 0.05).

In the first three months after the initial weight was recorded, the fish in group Cd had the

lowest TGC (1.47 ± 0.1) while group BW had the highest TGC (2.35 ± 0.1). For the

remainder of the trial, however, the fish in group Ca and Cd showed compensatory growth

and both groups had higher TGC values than groups BW and SF from July 2013 to

January 2014. Thus, there was no significant difference in the overall TGC among the

groups from April 2013 to January 2014 (two way nested ANOVA, P>0.05, Fig. 6).

17

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4/4/2013 - 10/7/2013 10/7/2013 - 9/10/2013 9/10/2013 - 14/1/2014 Overall

Ther

mal

grow

th co

effici

ent (

TGC)

ABCaCd

BW

SFCa

Cd nsaab

b

c

aabbb

aa

bb

Fig. 6. Thermal growth coefficient in Arctic charr subjected to different methods of SW acclimation. Means sharing the same letter are not significantly different at the 5% level. Data only includes fish that survived from start to finish.

3.2.3. Condition factor and sexual maturation

All groups had similar CF for the entire experiment, and significant difference was only

found between group BW and SF in October 2013 (Tukey HSD, P<0.05, Fig. 6.).

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

01/01/1900 02/01/1900 03/01/1900 04/01/1900

Con

ditio

n fa

ctor A

B

Ca

Cd

n.s

a

n.s

n.s

4/4/2013 10/7/2013 9/10/2013 14/1/2014

BW

SF

Ca

Cd

b ab ab

Fig. 7. Condition factors (CF) of Arctic charr given different acclimation to SW. Within each date, means sharing the same letter are not significantly different at the 5% level.

Male and female GSI was low among fish sampled for blood from April to October 2013

(<0.4%). Of the 240 individuals examined at the termination of the trial in January 2014,

only 11 fish had GSI above 2%. At that point the mean GSI in groups BW, SF, Ca and Cd

was 0.62 ± 0.27, 1.03 ± 0.38, 0.56 ± 0.28 and 0.40 ± 0.16 respectively, and was not

significantly different between groups (Two-way nested ANOVA, P>0.05).

18

3.2.4. Hypo-osmoregulatory ability

Group BW had significantly higher Gill NKA than group SF on 14 May 2013, two

months after transfer to SW (Tukey HSD, P < 0.05), and group Ca had significantly

higher NKA than group Cd after equally long period in SW (on 11 June). Thereafter, no

significant differences in gill NKA were found between groups.

In groups BW and SF there were significant positive linear relationships between NKA

sampled on 14 May 2013 and TGC in the period from 4 April to 14 May 2013 (Table 2).

No significant relationships were found between NKA and TGC in any group between

for the remainder of the experiment, except in the SF group where a significant

relationship was found between NKA on 22 January 2014 and TGC in the period from 9

October 2013 to 22 January 2014 (Table 2).

After two months in SW, significant differences were found in plasma Na+ between

groups BW and SF (May 2013), and between Ca and Cd (June 2013, Tukey HSD, P <

0.05). All groups showed similar plasma Na+ in October 2013, whereas in January 2014,

there were significant differences in plasma Na+ between all groups except SF and Cd.

0

2

4

6

8

10

12

14.5.2013 11.6.2013 9.10.2013 22.1.2014

Gill

Na+ ,

K+

AT

Pase

act

ivity

BW SF Ca Cd

150

155

160

165

170

175

180

185

190

14.5.2013 11.6.2013 9.10.2013 22.1.2014

Plas

ma

Na+

(mM

)

a a

bb

n.s

n.s

n.s

a

b

n.s

a

ab

b

c

(a)

(b)

Fig. 8. Mean + S.E. (a) gill Na+, K+, ATPase (NKA) and (b) plasma natrium in Salvelinus alpinus reared in SW following different SW acclimation methods. The first samples were taken after the fish had been kept in SW for two months, i.e. on 14 May for groups A and B and on 11 June for group Ca and Cd. Different lowercase letters indicate statistical difference at the 5% level.

19

Table 2. Relationships between branchial NKA activity and TGC over a preceding period. Regression coefficient of determination (r2) and slope (a). Asterisks (*) indicate significance of regression slope (P, t-test). **p < 0.01, n.s. = non-significant.

Growth period BW SF Ca Cd

4.4 - 14.5.2013

r2 0.28 0.52 - -a 0.36 0.41 - -P ** ** - -

4.4 - 11.6.2013

r2 - - 0.04 0.02a - - 0.12 0.17P - - n.s n.s

10.7 - 9.10.2013

r2 0.11 0.00 0.03 0.02a 0.13 0.07 0.07 -0.02P n.s n.s n.s n.s

9.10 - 14.1.2014

r2 0.07 0.41 0.01 0.00a 0.11 0.08 0.09 -0.13

P n.s ** n.s n.s

3.3. Experiment 2

3.3.1. Mortality and growth

The overall mortalities were low (1.9 – 2.7%) in all experimental groups. There were no

differences in mean weights between group BW and SF on 24 April, 27 June and 16

October 2013, whereas group C had significantly lower mean weight on all of these

sampling dates (Fig. 9. Tukey HSD, P<0.05). Group C showed the lowest growth (TGC)

in the period between 23 April and 27 June 2013. Thereafter, group C showed higher

TGC values than groups SF and C. Thus, the differences in the overall TGC values

among the groups were relatively small, or 2.41, 2.45 and 2.48 in groups BW, SF and C

respectively (Fig. 10).

20

0

200

400

600

800

1000

1200

1400

1600

Wei

ght (

g)

BWSFC

23/4/2013 27/6/2013 16/10/2013 31/1 - 12/2 - 6/3/2014

– – – –14/3/2013

3/4/201311/4/2013

b

aa

b

aa

aa

b

Fig. 9. Mean growth of Arctic charr subjected to different methods of acclimation to high salinity. The initial weight at the day of transfer to the experimental tanks was assessed from the combined weight of 100 individuals from each group, and thereafter by individual measurements. Mean sharing the same lowercase letters are not significantly different at the 5% level.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

23/4 - 27/6/2013 27/6 - 16/10/2013 16/10/2013 - Overall

The

rmal

gro

wth

coef

ficie

nt (T

GC

)

BW

SF

C

16/10/2013 - 31/1/201412/2/20146/3/2014

Fig. 10. Thermal growth coefficient in Arctic charr subjected to different methods of SW acclimation. As the initial mean weights and time of transfer to the experimental tanks was different among the groups, the time of harvesting was adjusted accordingly (indicated with coloured dates).

3.3.2. Condition factor and sexual maturation

In October 2013 there were no indications of sexual maturation in any group. At harvest,

in January to March 2014, only 4-7% of the 100 fish sampled from each group had GSI

above 1%, and the highest GSI was 3.7%.

21

Group SF had the highest body condition in the first two samplings in April and June

2013 while group BW and C showed similar CF. In October 2013, significant differences

were found between all groups, with the highest and lowest CF in groups BW and C

respectively (Tukey HSD, P<0.05). There were no significant differences in CF among

the groups at harvest (two-way nested ANOVA, P>0.05).

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

1 2 3 4

Con

ditio

n fa

ctor

BWSFC

ab b

a

abb

ab

c

n.s

23/4/2013 27/6/2013 16/10/2013 31/1/201412/2/2014

6/3/2014

Fig. 11. Mean + S.E. condition factor (CF) of Arctic charr subjected to different metods of SW acclimation. Means sharing the same lower case letter are not significantly different at the 5% level.


In October 2013 groups SF and C had significantly higher NKA than group BW (Tukey

HSD, P < 0.05). In February 2014, group C had the highest NKA whereas the NKA

activity among fish in groups BW and SF were similar, or 4.7 and 4.8 respectively (Fig.

11a). Plasma Na+ was not significantly different between groups in October 2013, but in

February, plasma Na+ was lowest in group BW, while no significant difference was found

between group SF and C (Fig. 11b, Tukey HSD, P>0.05).

22

0

1

2

3

4

5

6

7

8

9

16/10/2013 04/02/2014

Gill

Na+ ,

K+

AT

Pase

act

ivity

BWSFC

(a)

100

110

120

130

140

150

160

170

180

190

200

16/10/2013 04/02/2014

Plas

ma

Na+

(mM

)

(b)

aa

b

a

b b

n.sb

a a

Fig. 12. Mean + S.E. (a) gill Na+, K+, ATPase (NKA) and (b) plasma natrium in Arctic charr subjected to different method of SW acclimation. Samples were taken from fish reared at 26ppt. Different lowercase letters indicate statistical difference at the 5% level.

3.4. Experiment 3

3.4.1.Mortality, growth and feed conversion ratio

Overall group SF showed the best performance in regards to mortality (3.1%), growth

(TGC = 2.77) and FCR (1.20). The mortality rates in groups BW and C were similar, or

9.8 and 11.0% respectively. However, group C outperformed BW in both growth rate and

feed conversion (Table 3). In spite of higher performance in group SF compared with BW

and C, it can not be concluded that this is due to the supersmolt treatment, as the

mortality among fish in groups BW and C were unusually high for Arctic charr reared in

20ppt. Moreover, there were no differences between groups in experient 1 and 2.

23

Table 3. Initial and final mean weights (W1 and W2), thermal growth coefficient (TGC), number of fish harvested (n), mortality (M), feed conversion ratio (FCR) and mean temperature (T) in groups of Arctic charr at reared at 20 ppt after being subjected to different method of SW acclimation.

Group W1 W2 TGC1-2 n M (%) FCR T°C

BW 204 1387 2.32 36.386 9.8 1.25 5.8

SF 115 1116 2.77 38.949 3.1 1.20 5.7

C 100 1561 2.59 33.532 11.0 1.23 6.0


In October 2013, group BW showed significantly lower NKA activity compared with SF

and C (Tukey HSD, P<0.05), but no differences in NKA were found among the groups in

February 2014. In both sampling dates there were no significant differences in plasma

Na+ among the groups (Tukey HSD, P>0.05).

0

1

2

3

4

5

6

7

22/10/2013 03/02/2014

Gill

Na+ ,

K+

AT

Pase

act

ivity

BWSFC

aa

b

100

110

120

130

140

150

160

170

180

22/10/2013 03/02/2014

Plas

ma

Na+

(mM

)

n.s

n.s

n.s

(a)

(b)

Fig. 13. Mean + S.E. (a) gill Na+, K+, ATPase (NKA) and (b) plasma natrium in Arctic charr subjected to different method of SW acclimation. Samples were taken from fish

24

reared at 20ppt. Different lowercase letters indicate statistical difference at the 5% level

4. DiscussionIn the present study, Arctic charr juveniles reared under continuous photoperiod

(24L:0D) in slightly brackish water (3.7ppt), and juveniles given smolt-feed for 18 and 38

days in FW had higher gill NKA activity compared with a control group reared in FW.

The variation in mean NKA activity among the groups in this study was, however, not

predictive of their osmoregulatory performance in a 24h SW challenge test, as all groups

had similar plasma Na+ levels (overall mean = 180 ± 0.6 mM). In a recent study, Arctic

charr reared at 29 ppt showed similar plasma Na+ levels as the fish in this study, but were

nevertheless showing rapid growth and low mortality (1.9%) for over a year (Árnason et

al. 2014). Despite moderate plasma Na+ levels in the 24h SW challenge tests in current

study, however, the long-term survival in SW was relatively low, and most of the fish

that died in experiment 1 either lost weight or showed very low growth rates from the

time they entered SW until they died. In previous studies, plasma Na+ in Arctic charr has

been found to increase after the first day in SW (Arnesen et al. 1992, Bystriansky et al.

2006), and thus it is likely that more pronounced osmoregulatory disturbances would

have been detected if samples had been taken later than 24h after SW entry.

The current study shows that, in spite of lower gill NKA activity among Arctic charr

juveniles in group C (1.8±0.16) compared with groups BW (5.8±0.43) and SF (6.7±0.35)

at transfer to SW, there were no differences in long-term growth and survival in SW

when fish of similar initial sizes are compared. Body size was therefore the determining

factor for the growth and survival of the Arctic charr in the current study. The uniformity

in growth, survival and osmoregulatory capacity among the experimental groups was

somewhat unexpected, as no attempt was made to acclimatize group C for the entry to

SW. The explanation for this may be that the fish in group C had high gill NKA activity

on two sampling dates in February 2013, i.e. 62 and 43 days before transfer to SW

(overall mean NKA activity 4.7±0.26 μmol ADP · mg protein-1 ·h-1). Thus, in spite of the

relatively low NKA activity at the beginning of experiment1 compared with the activity

in February, it appears that many fish in group C were maintaining high

hypoosmoregulatory capacity, as large proportion of the fish in the upper size range were

showing relatively high long-term growth in SW. Similarly, Atlantic salmon show a

decrease in hypoosmoregulatory capacity two weeks after the peak of smolting, but

25

regain high hypoosmoregulatory capacity after five weeks (Mortensen & Damsgård,

1998).

Although wild anadromous Arctic charr are not expected to migrate to SW in February,

the increase in daylength during this time of winter seems the most plausible explanation

for the high NKA activity among fish in group C. Thus, the out-of-season development of

hypoosmoregulatory ability may have been initiated in late winter rather than spring, as

the fish were reared under continuous light which was superimposed on the much

brighter ambient light in the open outdoor tanks. The results from this study may

therefore have been different if the transfer from the juvenile facility at Öxnalækur to

higher salinities would have taken place at a different time of the year, e.g. in the autumn.

The Arctic charr in groups SF and C were reared under similar rearing conditions in the

juvenile facillity, and thus the fish in group SF were also found have relatively high NKA

activity in the first SW challenge test in February, i.e. one day before the supersmolt

treatment was initiated. However, NKA activity among fish in group SF was even higher

in March and therefore the supersmolt treatment prevented the reduction

hypoosmoregulatory ability which was seen in group C. The growth rate among fish

larger than 130 g in groups Ca and Cd were somewhat lower from April to July 2013

compared with fish of the same size-classes in groups BW and SF. This may to some

extent be attributed to lower NKA activity in group C prior to SW entry. However, as

mentioned before, NKA acivity at the beginning of the experiments was not predictive of

long-term growth performances in SW or in lower salinities. Moreover, NKA activity in

tagged individuals at the end of 68-97 day growth periods was generally not correlated

with growth rates (TGC) in the current study. Significant correlations were, however,

found when NKA activity was regressed against growth over 40 days. Thus, among fish

with hypoosmoregulatory ability sufficient to grow in high salinities, NKA activity had

short-term effects on growth. Similarly, although NKA activity may predict performances

during acute phase of acclimation to SW, Atlantic salmon smolts classified as having low

(0.6 to 4.3), middle (4.9 to 5.7) and high gill NKA activity (6.5 to 10.8 μmol ADP · mg

protein-1 ·h-1) at the peak of smolting in freshwater show the same performance in regards

to long-term growth and hypoosmoregulatory ability in seawater (Zydlewski &

Zydlewski, 2012).

In this study, as well as previous studies, body size profoundly influenced the salinity

tolerance of Arctic charr (Arnesen et al., 1992; Dempson, 1993). Although small-sized

wild anadromous Arctic charr may not develop hypoosmoregulaoty ability sufficient for

26

survival in SW, they have been found to show increased salinity tolerance and migratory

behaviour during spring (Nilssen and Gulseth, 1998). Small migrants, therefore, tend to

reside in FW or in the estuary and not in full strength SW (Moore 1975). However, in a

study on a Canadian Arctic charr strain, marine parasites were found on young charr that

were not ready for annual migration to the sea, thus suggesting that small Arcitc charr

may make short feeding excrusions into SW (Bouillon and Dempson 1989). The results

for the migratory behaviour of these wild Arctic charr correspond to the results in the

present study, where survival among small Arctic charr juveniles (<110 g) was high in

brackish water (20-26 ppt) in experiments 2 and 3, but much lower in 32 ppt in

experiment 1. Moreover, although the small fish that died in experiment 1 were not

growing, most of them were able to survive for weeks, even months after entering SW

and would therefore likely be capable of making short feeding excursions into seawater

like their wild Canadian counterparts. The highest mortality rates after transfer to SW

were found shortly after size measurements in July 2013, suggesting the fish were not

able to tolerate the additional stress associated with handling. Similarly, increased

mortality after handling under challenging salinity conditions have been reported for

Atlantic cod (Gadus morhua) and striped bass (Morene saxatilis) (Árnason et al., 2013;

Wallin & Van Den Avyle, 1995).

The size threshold at which Arctic charr develops the ability to grow and

hypoosmoregulate in full strength SW may be different among anadromous populations.

Gulseth et al. (2001) found that Arctic charr from Svalbard must have reached at least 25

cm before responding to photoperiodic cues triggering smoltification, whereas Arctic

charr juveniles as small as 20 cm from Northern Norway have been found to go through

parr-smolt transformation (Jørgenssen et al., 2007). Based on the present study, the Arctic

charr of the Holar strain must be relatively large if they are to be safely transferred from

FW or 3.7 ppt to SW. For group BW the overall survival rates plataued at around 90% in

fish larger than 160 g (~24 cm) and in contrast to smaller juveniles most of the large

juveniles had increased in size from the time they entered SW until they died. There was,

however, a great variation in salinity tolerance between individuals smaller than 160 g, as

some of the smallest juveniles (<80 g) were able hypoosmoregulate and grow in 32 ppt

while other equally sized or larger juveniles gained no weight and died in the weeks and

months following transfer to SW. The difference in hypoosmoregulatory ability is

therefore clearly influenced by more factors than body size.

27

In a recent study, 74 - 278 g (mean = 153 ± 3.2 g) Arctic charr of the same strain as

used in this study showed very low mortality and high growth rates for over a year after

direct transfer from 3.7 to 29 ppt (Árnason et al., 2014). Thus, 29 ppt seems to be close to

the upper limit for long-term salinity tolerance of ~80 g juveniles transferred directly

from 3.7ppt. The large difference in survival between 29 ppt in the study by Árnason et

al. (2014) and at 32 ppt in this study shows that relatively small differences in salinity

near full strength SW can have profound effects on the survival. It is therefore likely that

survival rates would have been lower if the salinity had been slightly higher than 32 ppt,

e.g. 35ppt.

In the SW challenge tests body size did not influence gill NKA activity in group SF,

However, in group C there was a significant positive correlation between body size and

NKA in two of the four challenge tests conducted for this group, and among the fish in

group BW, significant positive relationships between body size and gill NKA activity

were found in all three SW challenge tests. Moreover, at the start of experiment 1, it was

noted that several large juveniles in group BW were actively feeding only four hours after

the salinity was abruptly increased from 3.7 to 32 ppt. Although good appetite shortly

after exposure to SW indicates that some fish in group BW were well adapted for SW

entry, it is important to point out that they were significantly larger than those in groups

SF and C (Ca and Cd), and thus the fish in group SF and C may have behaved similarly if

they had been of similar size as in group BW.

In the present study, Arctic charr subjected to gradual transfer from FW to SW over a

period of six days (Group Ca) showed improved survival and growth compared to fish

directly transferred to SW (Group Cd). However, the growth enhancing effects of the

gradual acclimation were not permanent, as group Cd caught up with the fish in the Ca in

the long run. Gradual transfer from FW to SW during winter has also been found to

improve feed intake and growth in Norwegian Arctic charr compared to direct transfer

(Arnesen et al., 1993).

In conclusion, the study demonstrates that juveniles reared in slightly brackish water

under continuous light (group BW) and those given supersmolt feed in FW (group SF)

show higher gill NKA activity compared with those without supermolt feed under the

same conditions as group SF. However, in spite of differences in gill NKA activity at the

time of transfer to high salinities there were no differences in long-term growth and

survival when fish of similar sizes are compared between groups. No statistical

significance in mortality and growth between the control group (C) and those given

28

acclimation (BW and SF), is likely attributed to the high NKA activity among fish in

group C, 62 and 43 days before transfer to higher salinities. Thus, although no long-term

benefits of the BW and SF treatments were found, the results are somewhat inconclusive

as the hypoosmoregulatory ability may have been lower in the control group if the study

had been conducted earlier or later in the year. Body size was the determining factor for

the SW tolerance of the Arctic charr in this study.

References

Árnason, T., Gunnarsson, S., Imsland, A.K., Thorarensen, H., Smáradóttir, H.,

Steinarsson, A., Gústavsson, A, Johansson, M. (2014). Long-term rearing of Arctic

charr Salvelinus alpinus under different salinity regimes at constant temperature.

Journal of Fish Biology 85, 1145-1162.

Árnason, T., Magnadóttir, B., Björnsson, B., Steinarsson, A., Björnsson, B. Th. (2013).

Effects of salinity and temperature on growth, plasma ions, cortisol and immune

parameters of juvenile Atlantic cod (Gadus morhua). Aquaculture, 380-383, 70-79.

Arnesen, A.M., Halvorsen, M., Nilssen, K.J. (1992). Development of

hypoosmoregulatory capacity in Arctic charr (Salvelinus alpinus) reared under either

continuous light or natural photoperiod. Canadian Journal of Fisheries and Aquatic

Science 49, 229-237.

Arnesen, A.M., Jørgensen, E.H. and Jobling, M. (1994). Feed-growth relationships of

Arctic charr transferred from freshwater to seawater at different seasons. Aquaculture

International 2, 114-122.

Arnesen, A.M., Jørgensen, E.H., Jobling, M. (1993). Feed intake, growth and

osmoregulation in Arctic charr, Salvelinus alpinus (L.), transferred from freshwater

to saltwater at 8°C during summer and winter. Fish Physiology and Biochemistry 12,

281-292.

Boeuf, G. and Payan, P. (2001). How should salinity influence fish growth?

Comparative Biochemistry and Physiology C-Toxicology & Pharmalogy 130, 411-

423.

Bouillon, D.R. & Dempson, J.B. (1989). Metazoan parasite infections in landlocked and

anadromous Arctic charr (Salvelinus alpinus Linnaeus), and their use as indicators of

movement to sea in young anadromous charr. Canadian Journal of Zoology 67,

2478-2485.

29

Bystriansky, J.S., Richards, J.G., Schulte, P.M., Ballantyne, J.S. (2006). Reciprocal

expression of gill Na+/K+-ATPase α-subunit isoforms α1a and α1b during seawater

acclimation of three salmonid fishes that vary in their salinity tolerance. The Journal

of Experimental Biology 209, 1848-1858.

Dempson, J.B. 1993. Salinity tolerance of freshwater acclimated, small-sized Arctic

charr, Salvelinus alpinus from northern Labrador. Journal of Fish Biology 43, 451-

462.

Duston, J., Astatkie, T., Murray, S.B. (2007). Effect of salinity at constant 10°C on

grow-out of anadromous Arctic charr from Labrador. Aquaculture 273, 679-686.

Finstad, B., Nilsen, K.J. and Arnesen, A.M. (1989). Sesasonal changes in sea-water

tolerance of arctic charr (Salvelinus aplinus). Journal of Comparative Physiology B

159, 371-378.

Gulseth, O.A., Nilssen, K.J., Iversen, M., Finstand, B. (2001). Seawater tolerance in

first-time migrants of anadromous Arctic charr (Salvelinus alpinus). Polar biology

24, 270-275.

Gunnarsson, S., Johansson, M., Gústavsson, A., Árnason, T., Árnason, J., Smáradóttir,

H., Björnsson, B. Th., Thorarensen, H., Imsland, A.K. (2014). Effects of short-day

treatment on long-term growth performance and maturation of farmed Arctic charr

Salvelinus alpinus reared in brackish water. Journal of Fish biology 85, 1211-1226.

Jobling, M., Johnssen, H.K., Pettersson, G.W., Hendersson, R.J. (1993). Feeding,

growth and environmental requirements of Arctic charr: A review of aquaculture

potential. Aquaculture International 1, 20-46.

Johnsen, H.K., Eliassen, R.A., Sæther, B-S., Larsen, J.S. (2000). Effects of photoperiod

manipulation on development of seawater tolerance in Arctic charr. Aquaculture 189,

177-188.

Jørgensen, E.H., Øyvind, A-H., Moriyama, S., Iwata, M., Strand, J.E.T. (2007). The

parr-smolt transformation of Arctic charr is comparable to that of Atlantic salmon.

Aquaculture 273, 227-234.

McCormick, S.D. (1993). Methods for nonlethal gill biopsy and measurement of NA+,

K+ -ATPase activity. Canadian Journal of Fisheries and Aquatic Sciences 50, 565-

658.

McCormick, S.D. (2013). Smolt physiology and endocrinology. In Fish Physiology,

Vol. 32, Euryhaline Fishes (McCormick, S.D., Farrell, A.P. & Brauner, C.J., eds),

pp. 199-251. New York, NY: Acadmic Press.

30

Moore, J.W. (1975). Distribution, movements, and mortality of anadromous Arctic char,

Salvelinus alpinus L., in the Cumberland Sound area of Baffin Island. Journal of Fish

Biology 7, 339-348.

Mortensen, A. & Damsgård, B. (1998). The effect of salinity on desmoltification in

Atlantic salmon. Aquaculture 168, 407-411.

Nilssen, K.J. & Gulsteth, O.A. (1998). Summer seawater tolerance of small-sized

Arctic charr, Salvelinus alpius, on Svalbard. Polar Biology 20, 95-98.

Ojima, D., Pettersen, P.J., Wolkers, J., Johnsen, H.K. and Jorgensen, E.H. (2009).

Growth hormone and cortisol treatment stimulate seawater tolerance in both

anadromus and landlocked Arctic charr. Comparative Biochemistry and Physiology

A-Molecular & Integrative Physiology 153, 378-385.

Staurnes, M., Stigholt, T., Lysfjord, G. and Gulseth, O.A. (1992). Difference in the

seawater tolerance of anadromus and landlocked populations of Arctic charr

(Salvelinus alpinus). Canadian Journal of Fisheries & Aquatic Sciences 49, 443-452.

Þórður Flóventsson. 1929. Laxa og silungaklak á Íslandi. Fjölritunarstofa Pjeturs G.

Guðmundssonar. 192 p.

Wallin, J.E., & Van Den avyle, M.J. (1995). Interactive effects of stocking site salinity

and handling stress on survival of striped bass fingerlings. Transactions of the

American Fisheries Society 124, 736-745.

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Juvenile phase -acclimation

NúparHatchery

StaðurJuvenile station

3.7ppt

NúparHatchery

Gro

up B

W

ÖxnalækurJuvenile stationFW, Smolt-feed

Gro

up S

FG

roup

C

NúparHatchery

ÖxnalækurJuvenile station

FW, Control

Experiment 2 Hreidur 21-26ppt

Experiment 1 MRI, 32ppt

Experiment 3 Vatnsleysa 20ppt







Hatched: 1 – 14 February 2012

Hatched: 9 - 30 March 2012

Time of transfer Harvested

14.1.2014

14.1.2014

14.1.2014

31.1.2014

12.2.2014

6.3.2014

6 .5 – 13.5.2014

27.5 – 28.7.2014

3.2 – 24.3.2014

Egg – alevin

Hatched: 6 February – 14 April 2012

On-growing

Appendix 1. Experimental design in which Arctic charr were subjected to different methods of acclimation before transfer to intermediate and high salinities in experiments 1-3.

32

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