Journal of Fish Biology (2009) 75, 2695–2708doi:10.1111/j.1095-8649.2009.02468.x, available online at www.interscience.wiley.com

Digestive capacities, inbreeding and growth capacitiesin juvenile Arctic charr Salvelinus alpinus

D. Ditlecadet*†, P. U. Blier*, N. R. Le Francois*‡§ and F. Dufresne*

*Laboratoire de biologie integrative, Departement de biologie, chimie et geographie,Universite du Quebec a Rimouski, 300 allee des Ursulines, Rimouski, Quebec G5L 3A1,

Canada and ‡Biodome de Montreal, 4777, Avenue Pierre-De Coubertin, Montreal, QuebecH1V 1B3, Canada

(Received 23 June 2008, Accepted 25 September 2009)

Genetic variation in growth performance was estimated in 26 families from two commercial strainsof Arctic charr Salvelinus alpinus. Physiological determinants of growth and metabolic capacitieswere also assessed through enzymatic assays. A relatedness coefficient was attributed to each familyusing parental genotypes at seven microsatellite loci. After 15 months of growth, faster growingfamilies had significantly lower relatedness coefficients than slower growing families, suggestingtheir value as indicators of growth potential. Individual fish that exhibited higher trypsin activityalso displayed higher growth rate, suggesting that superior protein digestion capacities can be highlyadvantageous at early stages. Capacities to use amino acids as expressed by glutamate dehydrogenase(GDH) activities were lower in the liver of fast-growing fish (13–20%), whereas white muscle offast-growing fish showed higher activities than that of slow-growing fish for amino acid metabolismand aerobic capacity [22–32% increase for citrate synthase (CS), aspartate aminotransferase (AAT)and GDH]. The generally higher glycolytic capacities (PK and LDH) in white muscle of fast-growingfish indicated higher burst swimming capacities and hence better access to food. © 2009 The Authors

Journal compilation © 2009 The Fisheries Society of the British Isles

Key words: assimilation; digestion; growth rate; relatedness coefficient; metabolic capacities.

INTRODUCTION

Growth is a complex and energy requiring process for which a full understandingof the different physiological pathways dictating high growth is unavailable. Vari-ations of growth capacities early in the life of different fish species have beenshown to translate into important divergences in mass and size at later life stages(Imsland et al., 2007a, b). Identification of key physiological variables dictatinggrowth capacity at early stages and documenting the heritability of these variablesin fish populations could translate into promising selection targets and enable theoptimization of the growth trajectory of fish population or species.

§Author to whom correspondence should be addressed. Tel.: +1 514 868 3072; fax: +1 514 868 3065;email: NLe Francois@ville.montreal.qc.ca†Present address: Ocean Sciences Center, Memorial University of Newfoundland, St John’s, NewfoundlandA1C 5S7, Canada.

2695© 2009 The AuthorsJournal compilation © 2009 The Fisheries Society of the British Isles

2696 D . D I T L E C A D E T E T A L .

Proteolytic capacity of digestive system (mainly trypsin activity) has been shownto be an important physiological variable linked to growth rate in various species(Torrissen et al., 1994; Lemieux et al., 1999; Blier et al., 2007; Lamarre et al.,2007; Savoie et al., 2008). The relationship between digestive capacity, growth rateand metabolic capacity could possibly be highly significant at early stages. Indeed,Lemieux et al. (2003) have shown that growth rate increases once the ratio of trypsinover energetic metabolism enzymes reaches a threshold level in early life of Arcticcharr Salvelinus alpinus (L.). Later during the development, high energetic capacitycould provide a significant advantage by conferring higher locomotory capacities,and thus a better access to resources and a superior predator avoidance, as suggestedby Le Francois et al. (2005).

Various experimental manipulations have been proposed to obtain growth rate vari-ation in order to assess limiting factors involved in growth: temperature (Pelletieret al., 1993a, b, 1995; Overnell & Batty, 2000; Imsland et al., 2006; Savoie et al.,2008), growth hormone gene insertion (Stevens et al., 1999; Blier et al., 2002;Stevens & Devlin, 2005), food composition and ration level (Pelletier et al., 1994;Belanger et al., 2002; Lamarre et al., 2007). Another valuable approach to examinephysiological determinants of growth is to generate natural growth rate variation byrearing different families of a same species in a common environment. This type ofexperiment will ensure that the physiological differences will be caused by geneticrather than environmental effects.

Growth heterogeneity of S. alpinus is acknowledged to be an important limita-tion to the development of a sustainable industry based on this species in Canada(Tabachek & March, 1991; Rogers & Davidson, 2001), making this species a goodcandidate to generate natural growth rate variation within a given strain. Few studieshave taken advantage of strain divergences to gain insights into the physiologicalmechanisms underlying growth. Lemieux et al. (2003) used two strains of S. alpinusknown to have different growth performances, in order to explore the relationshipbetween digestive and metabolic capacities and growth performance early in devel-opment. Their study focused on early life stages (0–65 days post-hatch) and reliedon whole larvae enzymatic measurements, which did not allow the evaluation oftissue-specific response to observable growth differences.

The Fraser and the Buteux strains of S. alpinus are currently under investigationfor their potential for a selective breeding programme in Quebec, Canada (Ditlecadetet al., 2006). Using different families from these two strains reared in a commonenvironment, the present study aims to: (1) verify whether some families displaydifferent growth rates; (2) verify whether the degree of relatedness of the breedershas an effect on growth capacities; and (3) study the relationship between growthand enzyme activity through protein digestion (trypsin) and metabolic capacities[expressed by the activities of pyruvate kinase (PK), lactate dehydrogenase (LDH),citrate synthase (CS), aspartate aminotransferase (AAT) and glutamate dehydrogenase(GDH)] in target tissues (pyloric caeca, liver and white muscle).

MATERIALS AND METHODS

S T R A I N S BAC K G RO U N DAccess to breeders of the Fraser and Buteux strains was granted by the Pisciculture des

Alleghanys Inc., Ste Emelie-de-l’Energie, Quebec, Canada. The Fraser strain was developed

© 2009 The AuthorsJournal compilation © 2009 The Fisheries Society of the British Isles, Journal of Fish Biology 2009, 75, 2695–2708

D E T E R M I NA N T S O F G ROW T H R AT E I N S A LV E L I N U S A L P I N U S 2697

from eggs provided by the Rockwood Aquaculture Research Centre (Gunton, Manitoba,Canada) and grown at the Pisciculture des Alleghanys since the 1980s. The Buteux strainis the third generation of a hybrid between domesticated Fraser females and six males ofthe Lake Buteux population on the north of the St Lawrence, Quebec (Y. Boulanger, pers.comm.).

E X P E R I M E N T D E S I G NIn September 2002, 12 and 14 full-sib families were produced for the Fraser and the Buteux

strains, respectively. Adipose fins of all breeders were sampled and placed in 100% ethanolfor genotyping. Egg incubation took place at the Centre Aquacole Marin de Grande-Riviere(CAMGR) (Grande-Riviere, Quebec, Canada) until the eyed egg stage after which half of theeggs from each cross were transferred to a second experiment location (Aquaculture GaspesieInc., Gaspe, Quebec, Canada). Growth trials were conducted at two different sites to verifythat observed differences among families and strains were essentially due to actual genetic(and physiological) effects and not to different environmental conditions or rearing practices.Eggs from each family were incubated separately at 6◦ C in Heath tray incubators. Familieswere classified based on their hatching day to avoid large size variability at the beginningof the experiments. The families that hatched the earliest were classified as week1 and thelate hatchers as week2. Since eggs from the different families hatched at the same periodsat both locations, families were classified similarly as week1 (F1. . . F6 and B1. . . B7 forthe Fraser and the Buteux strains, respectively) or week2 (F7. . . F12 and B8. . . B14 for theFraser and the Buteux strains, respectively) families. Alevins were transferred into tanks atfirst feeding stage in March 2003. At the CAMGR, four groups were created by pooling 50alevins per family depending on the strain and on hatching day (week1-Fraser, week1-Buteux,week2-Fraser and week2-Buteux). At the Aquaculture Gaspesie facilities, where both strainswere mixed, two groups were created by pooling 100 alevins per family depending on thehatching day group (week1 and week2). Each group was reared in two tanks at both locationsto evaluate tank effect (A and B; Fig. 1). All experimental conditions (e.g. photoperiod,temperature, densities and food) were kept as identical as possible between both sites andchosen according to Johnston (2002).

Growth was monitored monthly in all tanks through mean mass estimations. Mean massmeasurements were made at regular intervals (CAMGR: 11 sampling times from April 2003to April 2004; Marinard: 10 sampling times from April 2003 to January 2004). In January2004, size variations were judged adequate to conduct two independent experiments.

E X P E R I M E N T 1 : G E N E T I C E F F E C T O N G ROW T HP E R F O R M A N C E ( C A M G R A N D AQ UAC U LT U R E G A S P E S I E )

In January 2004, the adipose fins of 20 and 50 fish of each tail (smallest and largest fish)were sampled in each tank at CAMGR and Aquaculture Gaspesie, respectively, and placed in100% ethanol for genotyping. The smallest fish were categorized as slow growers, whereasthe largest fish were categorized as fast growers. Mass of fish sampled at CAMGR in January2004 varied from 105·7 to 119·9 g and from 41·2 to 45·0 g in the upper and lower tails,respectively. At Aquaculture Gaspesie, mass varied from 187·2 to 209·4 g and from 69·7and 72·2 g in the upper and lower tails, respectively. The model developed for salmonids byIwama & Tautz (1981) was used to describe growth. A growth coefficient (Gc) was calculatedfor each fish sampled according to the formula: Gc = (W 0·3•

f − W 0·3•

i ) t−1 1000 T −1, whereT is the water temperature (◦ C), Wf is the final mass, Wi is the initial mass and t is theperiod of growth considered in days. As fish were too small to be tagged at the beginningof the experiment in April 2003, Wi used in the calculation corresponded to the mean massfor each tank in April 2003 after 1 month’s acclimation. The use of a mean mass for Wiintroduces a bias in the individual growth coefficient calculations but this bias was negligibleconsidering the small size variation at that time (mean ± mass 0·4 ± 0·1 g) and the lengthof the growth period considered (278 days).

© 2009 The AuthorsJournal compilation © 2009 The Fisheries Society of the British Isles, Journal of Fish Biology 2009, 75, 2695–2708

2698 D . D I T L E C A D E T E T A L .

Week1-AF1…F6 +B1…B7

(a)

(b)

Week1-BF1…F6 +B1…B7

Week2-AF7…F12 + B8…B14

Week2-BF7…F12 +B8…B14

Week1-Fraser-AF1…F6

Week1-Fraser-BF1…F6

Week1-Buteux-

AB1…B7

Week1-Buteux-

BB1…B7

Week2-Fraser-AF7…F12

Week2-Fraser-BF7…F12

Week2-Buteux-

AB8…B14

Week2-Buteux-

BB1…B14

Fig. 1. Experiment design at the (a) commercial (Aquaculture Gaspesie Inc., ) and (b) research stations(CAMGR, ) (in tanks A and B; F1 to F12 and B1 to B14 are Fraser and Salvelinus alpinus Buteuxfamilies, respectively).

Genotyping and family assignmentBreeders were genotyped at seven microsatellite loci known to be polymorphic in S. alpinus

and used in the evaluation of genetic variability of both strains in a previous study: Sco-19(Taylor et al., 2001), Mst-85 (Presa & Guyomard, 1996), Sfo-8, Sfo-18 and Sfo-23 (Angers& Bernatchez, 1996), Ogo-8 (Olsen et al., 1998) and Ssa-85 (Oreilly et al., 1996); the methodof Ditlecadet et al. (2006) was used in genotyping. From these genotypes, a relatedness coef-ficient (Rc) was estimated for each mating pair using KINSHIP 1.3.1 (Queller & Goodnight,1989). Values range from −1 to +1, high coefficients translating into high relatedness betweenmating pair under consideration. This coefficient has already proved to be a reliable tool todiscriminate relatives from unrelated individuals for turbot Psetta maxima (L.) (Borrell et al.,2004) and for both S. alpinus strains under study (Ditlecadet et al., 2006).

Only four of the seven microsatellites (Sfo-23, Sfo-8, Sco-19 and Mst-85) used for thebreeders genotyping were used for the parentage assignment of the fast and slow growerssince the three other loci were not informative. Parentage assignment was performed usingthe Probmax Parentage assignment programme 1.2 (Danzmann, 1997).

Family effect on growth performanceFamilies were classified as high growth or low growth according to the number of fish

in each tail (fast and slow grower individual fish). Only families with significant differencesbetween the number of fast and the number of slow growers were retained. Significanceof the number was measured with a χ2-test for each family comparing number of fast andslow growers observed with the theoretical numbers expected if there was no family effect.Families not classified in the same way in both duplicate tanks were not used. The sameprocedure was followed at each location.

Effect of breeders’ relatedness and growth performanceAll fish assigned to only one family were characterized by the respective Rc of their

genitors. ANOVA were performed for each group (week1, week2 at Aquaculture Gaspesie and

© 2009 The AuthorsJournal compilation © 2009 The Fisheries Society of the British Isles, Journal of Fish Biology 2009, 75, 2695–2708

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week1-Fraser, week2-Fraser, week1-Buteux, week2-Buteux at CAMGR) at each experimentlocation to measure the effect of Rc on the growth performance (represented by Gc). As eachgroup was duplicated at the two locations, the tank effect was tested using ANOVA.

E X P E R I M E N T 2 : D I G E S T I V E A N D M E TA B O L I C C A PAC I T I E SA N D G ROW T H ( C A M G R O N LY )

For this experiment, enzyme activities of fast growers sampled in January 2004 werecompared with slow growers sampled in April 2004. The slow growers thus had the samefinal mean mass than the fast growers but took more time to reach it (lower growth rates).This allowed enzyme activities to be compared between fast and slow growers eliminat-ing the important bias induced by fish size. It can therefore be assumed that variation inenzyme activities is driven by differences in growth rate rather than differences in size (Blieret al., 2002).

In January 2004, five of the fast growers were sacrificed in each tank and their liver,pyloric caeca and white muscle were sampled and kept at −80◦ C until enzymatic analyses.Fish were starved for 48 h before sampling. Small fish from the lower tail were passiveintegrated transponder (PIT) tagged and allowed to grow until April 2004 when their meanmass reached that of the larger fish sacrificed in January 2004. At this time, fish were sacrificedand sampled the same way as those from January 2004.

Digestive capacity was estimated through the measurement of trypsin activity in the pyloriccaeca. Metabolic capacities were also estimated since their activities have been repeatedlypositively linked to growth rate in several species (e.g. cod Gadus morhua L.: Pelletier et al.,1993b, 1994; spotted wolfish Anarhichas minor Olafsen: Imsland et al., 2006; Savoie et al.,2008). Activities of citrate synthase (CS), aspartate aminotransferase (AAT), glutamate dehy-drogenase (GDH), pyruvate kinase (PK) and lactate dehydrogenase (LDH) were measuredin pyloric caeca, liver and white muscle. Tissues were thawed on ice and homogenized innine volumes of Tris–HCl buffer (pH 7·5). Pyloric caeca homogenates were centrifuged at13 000 g for 15 min prior to trypsin analysis. All other tissues homogenates were centrifugedfor 30 s at 3000 g to eliminate tissue residuals. All enzyme activities were measured in dupli-cate with a Lambda 11 UV/VIS spectrophotometer (Perkin Elmer; www.perkinelmer.com) at15◦ C. The concentration of the extract was adjusted to provide a linear response for 5 min.The enzymes were assayed in the following order using these conditions: (1) CS (EC 4.1.3.7):100 mM Tris–HCl, 0·1 mM dithiobis-2-nitrobenzoic acid (DTNB), 0·1 mM acetyl CoA,0·15 mM oxaloacetate (omitted for the control), pH 8·0, (2) LDH (EC 1.1.1.27): 100 mMpotassium phosphate, 0·16 mM nicotinamide adenine dinucleotide hydrogenase (NADH),0·4 mM pyruvate (omitted for control), pH 7·0, (3) PK (EC 2.7.1.40): 50 mM imidazole-HCl, 10 mM MgCl2, 100 mM KCl, 5 mM ADP, 0·15 mM NADH, LDH in excess, 5·0 mMphosphoenolpyruvate, pH 7·0 (Pelletier et al., 1994), (4) AAT: 50 mM potassium phosphate,22 mM aspartate, 0·32 mM NADH, 0·025 mM pyridoxal phosphate, excess malate dehy-drogenase, 10 mM a-ketoglutarate, pH 7·4 (Pelletier et al., 1994), (5) GDH (E.C.1.4.1.2):100 mM Tris–HCl, 0·1 mM EDTA, 1·0 mM ADP, 250 mM ammonium acetate, 0·1 mMNADH, 14 mM a-ketoglutarate, pH 8·5 (Pelletier et al., 1994) and (6) trypsin (EC 3.4.4.4): amodification of the method of Preiser et al. (1975) was used. The substrate was prepared bydiluting 0·1 g of BAPNA (Sigma–Aldrich; www.sigmaaldrich.com) in 5 ml of dimethylfor-mamide (Torrissen et al., 1994). Then 50 µl of the substrate (final concentration 1 mg ml−1)was mixed with 930 µl of the buffer (0·2 M Tris–HCl, 0·04 M CaCl2, pH 8·4) before theaddition of 20 µl of enzyme solution. The assays for LDH, PK, AAT and GDH followedthe disappearance of NADH at 340 nm. CS was monitored at 412 nm to detect the transferof sulphydryl groups to 5, 5′ DTNB. Trypsin was monitored at 410 nm to detect the liber-ated p-nitroaniline. Extinction coefficients for NADH, DTNB and p-nitroaniline were 6·22,13·6 and 8·8 mM−1cm−1, respectively. Activities were expressed in unit per gram of tissue(U g−1

tissue).Three factors nested ANOVA were used to test for enzyme activity differences between

fast and slow growers using SYSTAT 10.2 (SYSTAT Software Inc.; www.systat.com.). Dueto the complexity of the experiment design, analyses were performed independently on each

© 2009 The AuthorsJournal compilation © 2009 The Fisheries Society of the British Isles, Journal of Fish Biology 2009, 75, 2695–2708

2700 D . D I T L E C A D E T E T A L .

hatching group. The three factors were strain, size and tanks. Tank duplicates (A and B) werenested within strain to take into account potential tank effect.

RESULTS

G ROW T H R AT E M O N I TO R I N G

Over the period considered, the relation between mass0·3•

and the time was linearwith r2 higher than 0·9 for all tanks as suggested by the model developed byIwama & Tautz (1981). The slopes were the same for all tanks at CAMGR whateverthe strain (Fraser or Buteux) or the hatching group. At Aquaculture Gaspesie, theslope was different for one tank of the week2 group, this tank displayed a lowergrowth rate than the three others. A significant difference of growth rate was observedbetween the two experiment stations, Aquaculture Gaspesie displaying the highestgrowth rates.

E X P E R I M E N T 1 : G E N E T I C E F F E C T O N G ROW T HP E R F O R M A N C E ( C A M G R A N D AQ UAC U LT U R E G A S P E S I E )

The values of Gc of fast and slow growers are shown in Table I. At CAMGR, Gcof fast growers were significantly higher than slow growers in all tanks (ANOVA,F1,303, P < 0·001). No effect of the strain or of the hatching group was detected. AtAquaculture Gaspesie, Gc of fast growers were also significantly higher than slowgrowers in all tanks (ANOVA, F1,392, P < 0·001). A difference in Gc was notedbetween the fast growers, one of the week2 tank displaying a lower Gc than thethree others. The Gc displayed at Aquaculture Gaspesie was all higher than those atCAMGR.

Table I. Growth coefficients (Gc) of fast and slow growers for each tank (A and B) and strain(Fraser and the Buteux) at each experiment site, Centre Aquacole Marin de Grande-Riviere(CAMGR) and Aquaculture Gaspesie. Data shown correspond to mean ± s.d. (n = 20 and

50 per tank and per size group for CAMGR and Aquaculture Gaspesie, respectively)

Gc

Experiment location Tank Fast growers Slow growers

CAMGR Week1-FraserA 1·237 ± 0·054 0·893 ± 0·098Week1-FraserB 1·220 ± 0·087 0·908 ± 0·092Week1-ButeuxA 1·256 ± 0·073 0·827 ± 0·119Week1-ButeuxB 1·196 ± 0·067 0·898 ± 0·095Week2-FraserA 1·240 ± 0·063 0·949 ± 0·117Week2-FraserB 1·189 ± 0·077 0·892 ± 0·116Week2-ButeuxA 1·250 ± 0·072 0·904 ± 0·092Week2-ButeuxB 1·272 ± 0·090 0·882 ± 0·010

Aquaculture Gaspesie Week1-A (mixed) 1·553 ± 0·074 1·036 ± 0·122Week1-B (mixed) 1·604 ± 0·087 1·027 ± 0·146Week2-A (mixed) 1·503 ± 0·109 1·005 ± 0·151Week2-B (mixed) 1·367 ± 0·079 0·990 ± 0·128

© 2009 The AuthorsJournal compilation © 2009 The Fisheries Society of the British Isles, Journal of Fish Biology 2009, 75, 2695–2708

D E T E R M I NA N T S O F G ROW T H R AT E I N S A LV E L I N U S A L P I N U S 2701

Table II. Relatedness coefficients (Rc) of each Salvelinus alpinus family of the Fraser(F) and Buteux strains (B)

Fraser Buteux

Hatching group Family Rc Family Rc

Week1 F1 0·295 B1 –0·274F2 0·144 B2 –0·040F3 0·066 B3 0·169F4 –0·531 B4 –0·324F5 –0·607 B5 –0·070F6 0·123 B6 0·389

B7 –0·186Week2 F7 0·364 B8 0·360

F8 –0·387 B9 –0·174F9 0·197 B10 0·050F10 –0·285 B11 0·272F11 –0·514 B12 –0·415F12 –0·116 B13 0·370

B14 0·286

Relatedness estimation of breeder pairsThe Rc of each family used in this study is shown in Table II. Values varied from

−0·607 to 0·364 and from −0·415 to 0·389 for the Fraser and the Buteux strains,respectively.

Microsatellites and parentage assignmentSeventy per cent of all genotyped offspring could be matched to one family, 20·9%

to two families and 7·2% to more than three families. One per cent was assignedto families not present in the tank. These fish most probably transferred from otherdrawers in the incubation unit during the hatching stage.

Growth performance and family effectAt the Aquaculture Gaspesie facility, only eight of the 26 total families (13 families

per group, both strain mixed) were retained and classified as high growth (generallyexhibiting higher growth rate) or low growth (generally exhibited lower growth rate).All high-growth families were from the Buteux strain. Low-growth families from theweek1 group were all from the Fraser strain, whereas those from the week2 groupwere all from the Buteux strain (Table III). At the CAMGR, only seven of the 26total families (six families per group for the Fraser strain and seven families pergroup for the Buteux strain) were retained (Table II). Four of these families (B12,F1, F2 and B14) have also been detected at Aquaculture Gaspesie and were simi-larly classified. Family B7 was classified as low growth at the CAMGR, whereas itwas classified as high growth at Marinard. Two families from the Fraser strain wereassigned as high growth at the CAMGR, whereas no families of this strain wereassigned as high growth at Aquaculture Gaspesie.

© 2009 The AuthorsJournal compilation © 2009 The Fisheries Society of the British Isles, Journal of Fish Biology 2009, 75, 2695–2708

2702 D . D I T L E C A D E T E T A L .

Table III. Buteux (B) and Fraser (F) Salvelinus alpinus families classified as high growthor low growth for each group in each experiment site. In Centre Aquacole Marin de Grande-Riviere (CAMGR), both strains are separated while they are mixed in Aquaculture Gaspesie

Experiment location Group High growth Low growth

CAMGR (research station) Week1-Fraser F4 F1. F2Week1-Buteux None B7Week2-Fraser F8 NoneWeek2-Buteux B12 B14

Aquaculture Gaspesie Week1 B1. B2. B7 F1. F2(commercial station)

Week2 B12 B11. B14

Growth performance and relatedness coefficient (Rc)At Aquaculture Gaspesie, a tank effect was detected for both group considered

(week1 and week2). A significant effect of Rc on growth performance, however,was detected in all tanks with the fast growers displaying lower Rc values (ANOVA,F1,149, P < 0·001 and F1,127, P < 0·001 for week1 and week2 groups, respectively).

At CAMGR, no tank effects were detected. A significant effect of Rc on growthperformance was again detected in two groups, the fast growers still displaying lowerRc (ANOVA, F1,54, P < 0·001 and F1,51, P < 0·001 for week1-Fraser and week2-Buteux, respectively). No significant effect was detected for the two other groups(ANOVA, F1,55, P > 0·05 and F1,57, P > 0·05 for week2-Fraser and week1-Buteux,respectively).

E X P E R I M E N T 2 : D I G E S T I V E A N D M E TA B O L I C C A PAC I T I E SA N D G ROW T H ( C A M G R O N LY )

Enzymatic activity in pyloric caecaDifferences in enzyme activities between fast and slow growers were detected for

trypsin (Table IV). Trypsin activities were higher in fast growers from both strainsfor the week2 hatching group (ANOVA, F1,30, P < 0·001) and in the Buteux strainfrom the week1 group (ANOVA, F1,2, P < 0·05). A tank effect was detected on theactivity of trypsin for the Fraser strain of the week1 group. No clear effect of thestrain was observed.

Enzymatic activity in liverDifferences in enzyme activities between fast and slow growers were only detected

for GDH (Table IV). A significant higher activity of GDH was detected for bothstrains in the week2 group (ANOVA, F1,32, P < 0·001). No effect of the strain wasobserved.

Enzymatic activity in white muscleSignificant differences in enzyme activities were detected in white muscle between

fast and slow growers (Table IV). CS, AAT and GDH all exhibited higher activities infast growers for both strains of week1 (ANOVA, F1,31, P < 0·001, F1,30, P < 0·001and F1,31, P < 0·001 for CS, AAT and GDH, respectively). The same differences

© 2009 The AuthorsJournal compilation © 2009 The Fisheries Society of the British Isles, Journal of Fish Biology 2009, 75, 2695–2708

D E T E R M I NA N T S O F G ROW T H R AT E I N S A LV E L I N U S A L P I N U S 2703

Tab

leIV

.E

nzym

eac

tiviti

esin

units

per

gram

oftis

sue

(mea

n±

s.d.

)of

Salv

elin

usal

pinu

sfa

stan

dsl

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ower

sfo

rea

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oup

and

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hen

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fect

was

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cted

are

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Wee

k2-F

rase

rW

eek2

-But

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Tiss

ueE

nzym

eFa

stSl

owFa

stSl

owFa

stSl

owFa

stSl

ow

Pylo

ric

caec

aC

S4·

0±

1·4

5·0

±1·

14·

5±

0·7

5·4

±1·

25·

6±

0·9

4·6

±1·

65·

3±

1·2

5·2

±1·

5A

AT

7·1

±0·

77·

0±

1·5

7·5

±0·

38·

0±

0·9

8·2

±1·

58·

0±

1·4

7·5

±0·

98·

2±

0·6

Tryp

sin

——

4·9

±0·

8∗3·

9±

1·0∗

7·9

±1·

9∗4·

9±

1·2∗

6·6

±1·

5∗4·

0±

0·7∗

Liv

erC

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8±

0·9

5·2

±1·

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3±

0·8

5·0

±0·

74·

6±

0·6

5·5

±1·

04·

5±

0·8

5·0

±0·

8A

AT

56·0

±7·

955

·4±

4·3

58·3

±11

·753

·1±

7·4

54·4

±6·

355

·5±

6·8

53·0

±8·

456

·3±

4·8

GD

H76

·8±

11·9

82·6

±12

·574

·1±

9·2

72·7

±8·

676

·6±

9·2∗

88·1

±11

·2∗

71·7

±14

·4∗

89·5

±13

·9∗

PK44

·0±

12·9

43·9

±13

·745

·5±

10·8

41·7

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16·9

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© 2009 The AuthorsJournal compilation © 2009 The Fisheries Society of the British Isles, Journal of Fish Biology 2009, 75, 2695–2708

2704 D . D I T L E C A D E T E T A L .

were observed for the Buteux strain of the week2 group (ANOVA, F1,16, P < 0·01,F1,16, P < 0·001 and F1,16, P < 0·001 for CS, AAT and GDH, respectively). Nodifferences were detected for PK. For LDH, no significant effect of the growthperformance was detected due to a tank effect. Trends observed in all tanks, however,were always for a higher activity in fast growers. No effect of the strain was observedin this tissue.

DISCUSSION

G ROW T H C O M PA R I S O N B E T W E E N S T R A I N S

At CAMGR, both strains were kept separated which allowed their growth to becompared. Mean growth rate was the same in all tanks with no effect of the strain(Buteux and Fraser) or of the hatching group (week1 and week2). This observationis not surprising since the Buteux strain is the third generation of a hybrid betweendomesticated Fraser females and only six males of Lake Buteux. The strains aretherefore very closely related, which may explain their similar mean growth rate. Theobserved growth rates are in the same range as those displayed by other salmonidsspecies (Iwama & Tautz, 1981). At Aquaculture Gaspesie where both strains weremixed, fish from a single tank had lower mean growth rate than those from the threeother tanks but in all cases mean growth rates were all higher at Aquaculture Gaspesiethan at CAMGR. Rearing conditions were kept as similar as possible between bothexperiment locations (feed, rearing practices and light conditions) so, difference mayhave occurred through differences in water quality.

G E N E T I C E F F E C T S O N G ROW T H C A PAC I T I E S

Concerning the effect of genetics on growth performance, two hypotheses wereaddressed with the first experiment: (1) some families grow faster than others and(2) fast growers are produced from more distant crosses. Only eight and seven ofthe 26 families were categorized as high growth or low growth at AquacultureGaspesie and CAMGR, respectively. Four of these families performed similarly atboth locations, thus suggesting that their growth potential was dictated by markedgenetic differences. All high-growth families detected at Aquaculture Gaspesie werefrom the Buteux strain. At CAMGR, where both strains were separated, one Fraserstrain family was categorized as high growth in both of week1 and week2 groupssuggesting the possibility of aggressive behaviour of the Buteux strain towards theFraser strain when both strains are mixed (Aquaculture Gaspesie). A poor correlationbetween family growth performances in single-tank and in mixed-tank environmenthas already been observed for Atlantic salmon Salmo salar L. (Herbinger et al.,1999). The authors suggested that different growth capacities might reflect envi-ronmental differences among tanks rather than genetic differences among families.Important differences due to genetic and environment interactions among familiescould also be suspected (Cote et al., 2007).

An interesting negative correlation was observed between Rc and growth rate in alltanks at Aquaculture Gaspesie. The same negative correlations were observed in twogroups at CAMGR (week1-Fraser and week2-Buteux). Fish from more related fam-ilies displayed generally lower Gc. This is in accord with results of Herbinger et al.

© 2009 The AuthorsJournal compilation © 2009 The Fisheries Society of the British Isles, Journal of Fish Biology 2009, 75, 2695–2708

D E T E R M I NA N T S O F G ROW T H R AT E I N S A LV E L I N U S A L P I N U S 2705

(1995), which found insights into depressed growth capacities due to inbreeding inrainbow trout Onchorynchus mykiss (Walbaum). This intriguing result is strengthenedby the relatedness coefficients exhibited by the families characterized as high-growthor low-growth families. High-growth families had negative Rc, whereas most of thelow-growth families had Rc > 0·14 suggesting their high degree of parentage. Fam-ily B7 was the only exception to this pattern and was categorized oppositely at bothsites. These results are of primary relevance for commercial growers since it couldallow them to significantly enhance their production using only breeder’s genotypes.Further experiments should thus be performed to validate these results. Consideringthis result, the Buteux strain could be a better choice for the initiation of a selectionprogramme since it is genetically more variable than the Fraser strain (Ditlecadetet al., 2006).

G ROW T H A N D D I G E S T I V E C A PAC I T I E S

The most important result that was obtained was the much higher trypsin activityin fast growers from three groups out of four. Trypsin is a key enzyme involvedin protein digestion in fishes (Ueberschar, 1988) since it acts directly and indirectlythrough chymotrypsin activation in protein digestion. Correlation of trypsin activi-ties with growth rate and food conversion efficiency has been previously observedin G. morhua (Lemieux et al., 1999; Belanger et al., 2002; Blier et al., 2007). InS. salar, Stevens et al. (1999) showed an important increase in the size of the pyloriccaeca of GH-transgenic fish. These displayed a higher growth rate in comparison withnon-transgenic fish. In another study on S. salar, trypsin appeared to be the key pro-tease under conditions favouring growth (Rungruangsak-Torrissen et al., 2006). Thepresent results are therefore consistent with what has been found in other speciesbut also reveal that differences in proteolytic capacity at early stages in fishes rearedin common environment can lead to significant divergences in mass gain in the firstmonths after hatching. This could be of major significance because this period isa critical step where the largest part of size discrepancy and mortality occurs. Ifquickly reaching critical mass could ensure higher survival probability, divergencein proteolytic capacity among families or population could probably be an efficienttarget for selective process (natural or artificial).

G ROW T H A N D M E TA B O L I C C A PAC I T I E S

Differences in enzyme activities between fast and slow growers were detected forGDH in liver, and CS, AAT and GDH, in white muscle. A trend was only notedfor PK and LDH in all groups with fast growers always presenting higher activi-ties than slow growers. All enzymes investigated in white muscle were higher forthe fast growers, whereas GDH assayed in liver were higher for the slow growers.Liver is known to have a high metabolic and protein turnover rate. In the presentstudy, S. alpinus with the lowest growth performance (slow growers) displayed thehighest GDH activities. The GDH can be associated with anabolism or catabolism:it catalyses both the reversible conversion of ammonium nitrogen into organic nitro-gen (glutamate production) and the oxidative deamination of glutamate resultingin 2-oxoglutarate (Timmerman et al., 2003). Dobly et al. (2004) have shown thatO. mykiss displaying poor growth efficiency also had higher rates of protein turnover

© 2009 The AuthorsJournal compilation © 2009 The Fisheries Society of the British Isles, Journal of Fish Biology 2009, 75, 2695–2708

2706 D . D I T L E C A D E T E T A L .

in the liver. In parallel, they showed that non-digestive proteolytic enzyme activitieswere lower in fish with high specific growth rates. This suggests that hepatic GDHis important by providing amino acid in fishes that can hardly rely on alimentaryproteins. The present results agree with this previous study if the catabolic functionof GDH in liver is considered. In white muscle, higher GDH and AAT activities infast-growing fish may be linked to high activity of amino acid transamination andprotein deposition. Both protein synthesis and protein degradation are energeticallydemanding processes and have to be sustained by energetic metabolism (Houlihanet al., 1995), which might explain the higher CS activities observed. The strong trendfor fast growers to display higher activities for PK and LDH is also interesting. Suchresults have been shown in various studies on G. morhua (Pelletier et al., 1993a,b, 1994, 1995; Couture et al., 1998). LDH is involved in anaerobic glycolysis andhas been used as an index of fish capacity for burst swimming (Somero & Chil-dress, 1980). The increase in muscle glycolytic enzyme activities with growth ratecould further improve growth capacity if this one is limited by resources access. Thegreater burst swimming capacity could enhance locomotion capacity of fishes (andprovide better access to food and greater predator avoidance Pelletier et al., 1994:G. morhua; Le Francois et al., 2005: S. alpinus).

To conclude, the results indicate that: (1) some families displayed faster growththan others, (2) fish displaying the highest growth rate (fast growers) were generallyproduced from more distant crosses and (3) fish displaying the highest growth rate(fast growers) displayed higher digestive and metabolic capacities than fish displayingthe lowest growth rate (slow growers). The experimental design did not allow a directlink between Rc and enzyme activities to be made. The strongest evidence from thestudy is that digestive protease activity in pyloric caeca (trypsin) highly correlateswith growth rate at early stages.

This work was funded by the Conseil des Recherches en Peche et en Agroalimentaire duQuebec (CORPAQ) and the Fondation de l’Universite du Quebec a Rimouski (FUQAR) toF.D., P.U.B. and N.R.L.F. The authors want to express their gratitude to Y. Boulanger ofthe Pisciculture des Alleghanys Inc., F. Dupuis of Aquaculture Gaspesie Inc. and T. Grenier(UQAR/MAPAQ) for their technical support.

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