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Growth reaction norms of domesticated, wild and hybrid Atlantic salmon families in response to differing social and physical environments.

Solberg MF, Zhang Z, Nilsen F, Glover KA - BMC Evol. Biol. (2013)

Bottom Line: The main results of this study, which are based upon the analysis of more than 6000 juvenile salmon, can be summarised as; (i) there was no difference in relative growth between wild and farmed salmon when reared together and separately; (ii) the relative difference in body weight at termination between wild and farmed salmon decreased as mortality increased along the environmental gradient approaching natural conditions.This study demonstrates that potential social interactions between wild and farmed salmon when reared communally are not likely to cause an overestimation of the genetic growth differences between them.Therefore, common-garden experiments represent a valid methodological approach to investigate genetic differences between wild and farmed salmon.

View Article: PubMed Central - HTML - PubMed

Affiliation: Section of Population Genetics and Ecology, Institute of Marine Research, P,O, Box 1870, Nordnes, NO-5817 Bergen, Norway. monica.solberg@imr.no.

ABSTRACT

Background: Directional selection for growth has resulted in the 9-10th generation of domesticated Atlantic salmon Salmo salar L. outgrowing wild salmon by a ratio of approximately 3:1 when reared under standard hatchery conditions. In the wild however, growth of domesticated and wild salmon is more similar, and seems to differ at the most by a ratio of 1.25:1. Comparative studies of quantitative traits in farmed and wild salmon are often performed by the use of common-garden experiments where salmon of all origins are reared together to avoid origin-specific environmental differences. As social interaction may influence growth, the large observed difference in growth between wild and domesticated salmon in the hatchery may not be entirely genetically based, but inflated by inter-strain competition. This study had two primary aims: (i) investigate the effect of social interaction and inter-strain competition in common-garden experiments, by comparing the relative growth of farmed, hybrid and wild salmon when reared together and separately; (ii) investigate the competitive balance between wild and farmed salmon by comparing their norm of reaction for survival and growth along an environmental gradient ranging from standard hatchery conditions to a semi-natural environment with restricted feed.

Results: The main results of this study, which are based upon the analysis of more than 6000 juvenile salmon, can be summarised as; (i) there was no difference in relative growth between wild and farmed salmon when reared together and separately; (ii) the relative difference in body weight at termination between wild and farmed salmon decreased as mortality increased along the environmental gradient approaching natural conditions.

Conclusions: This study demonstrates that potential social interactions between wild and farmed salmon when reared communally are not likely to cause an overestimation of the genetic growth differences between them. Therefore, common-garden experiments represent a valid methodological approach to investigate genetic differences between wild and farmed salmon. As growth of surviving salmon of all origins became more similar as mortality increased along the environmental gradient approaching natural conditions, a hypothesis is presented suggesting that size-selective mortality is a possible factor reducing growth differences between these groups in the wild.

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Overview of the experimental design, experiment I. The experimental period lasted for 44 weeks. Sampled individuals were sorted into smolts and non-smolts, based upon size and parr markings, and in the mixed-strain treatments and the single-strain treatment individuals were randomly sampled until 500 and 150 smolts, respectively, were sampled from each treatment tank. Out of the 3027 individuals sampled, 61 individuals were removed due to unsuccessful family assignment, growth malformations or sampling errors, leaving the total data set for growth comparisons consisting of 2966 individuals. The single-strain treatment initially consisted of three replicates per origin. However, to control for increasing biomasses these replicates were thinned as being merged into two replicates, where one replicate were later terminated due to rearing capacity.
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Figure 1: Overview of the experimental design, experiment I. The experimental period lasted for 44 weeks. Sampled individuals were sorted into smolts and non-smolts, based upon size and parr markings, and in the mixed-strain treatments and the single-strain treatment individuals were randomly sampled until 500 and 150 smolts, respectively, were sampled from each treatment tank. Out of the 3027 individuals sampled, 61 individuals were removed due to unsuccessful family assignment, growth malformations or sampling errors, leaving the total data set for growth comparisons consisting of 2966 individuals. The single-strain treatment initially consisted of three replicates per origin. However, to control for increasing biomasses these replicates were thinned as being merged into two replicates, where one replicate were later terminated due to rearing capacity.

Mentions: All 30 families were incubated in single-family units until the eyed-egg stage. Dead eggs were picked daily and then shocked on January 31, 2011, to sort out dead eggs. One wild family was at this point excluded from the study, due to high egg mortality. Hence, the farmed, hybrid and wild origins were represented with 10:10:9 families respectively. Measurement of eggs from all families (diameter in mm) were taken on February 18, 2011. On February 22, 2011, fertilized eggs were sorted into the two experiments (FiguresĀ 1 and 2).


Growth reaction norms of domesticated, wild and hybrid Atlantic salmon families in response to differing social and physical environments.

Solberg MF, Zhang Z, Nilsen F, Glover KA - BMC Evol. Biol. (2013)

Overview of the experimental design, experiment I. The experimental period lasted for 44 weeks. Sampled individuals were sorted into smolts and non-smolts, based upon size and parr markings, and in the mixed-strain treatments and the single-strain treatment individuals were randomly sampled until 500 and 150 smolts, respectively, were sampled from each treatment tank. Out of the 3027 individuals sampled, 61 individuals were removed due to unsuccessful family assignment, growth malformations or sampling errors, leaving the total data set for growth comparisons consisting of 2966 individuals. The single-strain treatment initially consisted of three replicates per origin. However, to control for increasing biomasses these replicates were thinned as being merged into two replicates, where one replicate were later terminated due to rearing capacity.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4231500&req=5

Figure 1: Overview of the experimental design, experiment I. The experimental period lasted for 44 weeks. Sampled individuals were sorted into smolts and non-smolts, based upon size and parr markings, and in the mixed-strain treatments and the single-strain treatment individuals were randomly sampled until 500 and 150 smolts, respectively, were sampled from each treatment tank. Out of the 3027 individuals sampled, 61 individuals were removed due to unsuccessful family assignment, growth malformations or sampling errors, leaving the total data set for growth comparisons consisting of 2966 individuals. The single-strain treatment initially consisted of three replicates per origin. However, to control for increasing biomasses these replicates were thinned as being merged into two replicates, where one replicate were later terminated due to rearing capacity.
Mentions: All 30 families were incubated in single-family units until the eyed-egg stage. Dead eggs were picked daily and then shocked on January 31, 2011, to sort out dead eggs. One wild family was at this point excluded from the study, due to high egg mortality. Hence, the farmed, hybrid and wild origins were represented with 10:10:9 families respectively. Measurement of eggs from all families (diameter in mm) were taken on February 18, 2011. On February 22, 2011, fertilized eggs were sorted into the two experiments (FiguresĀ 1 and 2).

Bottom Line: The main results of this study, which are based upon the analysis of more than 6000 juvenile salmon, can be summarised as; (i) there was no difference in relative growth between wild and farmed salmon when reared together and separately; (ii) the relative difference in body weight at termination between wild and farmed salmon decreased as mortality increased along the environmental gradient approaching natural conditions.This study demonstrates that potential social interactions between wild and farmed salmon when reared communally are not likely to cause an overestimation of the genetic growth differences between them.Therefore, common-garden experiments represent a valid methodological approach to investigate genetic differences between wild and farmed salmon.

View Article: PubMed Central - HTML - PubMed

Affiliation: Section of Population Genetics and Ecology, Institute of Marine Research, P,O, Box 1870, Nordnes, NO-5817 Bergen, Norway. monica.solberg@imr.no.

ABSTRACT

Background: Directional selection for growth has resulted in the 9-10th generation of domesticated Atlantic salmon Salmo salar L. outgrowing wild salmon by a ratio of approximately 3:1 when reared under standard hatchery conditions. In the wild however, growth of domesticated and wild salmon is more similar, and seems to differ at the most by a ratio of 1.25:1. Comparative studies of quantitative traits in farmed and wild salmon are often performed by the use of common-garden experiments where salmon of all origins are reared together to avoid origin-specific environmental differences. As social interaction may influence growth, the large observed difference in growth between wild and domesticated salmon in the hatchery may not be entirely genetically based, but inflated by inter-strain competition. This study had two primary aims: (i) investigate the effect of social interaction and inter-strain competition in common-garden experiments, by comparing the relative growth of farmed, hybrid and wild salmon when reared together and separately; (ii) investigate the competitive balance between wild and farmed salmon by comparing their norm of reaction for survival and growth along an environmental gradient ranging from standard hatchery conditions to a semi-natural environment with restricted feed.

Results: The main results of this study, which are based upon the analysis of more than 6000 juvenile salmon, can be summarised as; (i) there was no difference in relative growth between wild and farmed salmon when reared together and separately; (ii) the relative difference in body weight at termination between wild and farmed salmon decreased as mortality increased along the environmental gradient approaching natural conditions.

Conclusions: This study demonstrates that potential social interactions between wild and farmed salmon when reared communally are not likely to cause an overestimation of the genetic growth differences between them. Therefore, common-garden experiments represent a valid methodological approach to investigate genetic differences between wild and farmed salmon. As growth of surviving salmon of all origins became more similar as mortality increased along the environmental gradient approaching natural conditions, a hypothesis is presented suggesting that size-selective mortality is a possible factor reducing growth differences between these groups in the wild.

Show MeSH
Related in: MedlinePlus