Development of an Atlantic salmon (Salmo salar) genetic improvement program: Genetic parameters of harvest body weight and carcass quality traits estimated with animal models
Introduction
The Atlantic Salmon Broodstock Development Program (ASBDP) is a partnership of researchers and commercial producers based in St. Andrew's, New Brunswick, Canada that aims to develop a genetically-improved strain of Atlantic salmon for commercial aquaculture in Atlantic Canada. The goal of the breeding program is to develop salmon with an optimal combination of fast growth rate, good carcass quality, and low incidence of early sexual maturation.
Under current New Brunswick government regulations, only Atlantic salmon descended from the wild population of the Saint John River, New Brunswick can be cultured; therefore, genetic improvement of cultured salmon must rely on selection and breeding within this strain. Genetic parameters for traits in this population, and specifically for the ASBDP stock, must therefore be estimated to predict how the ASBDP stock will respond to various selection and breeding techniques.
Growth rate has generally been the trait of highest economic importance in meat livestock improvement programs and this is also the case in Atlantic salmon culture. Body weight at a fixed age has frequently been used as an indicator of growth rate in aquaculture and, additionally, body weight at harvest determines the price paid to growers by processors. Studies have generally found harvest-age (2–3.5 years) body weights in Atlantic salmon to have moderate heritability (Gunnes and Gjedrem, 1978, Gjerde and Gjedrem, 1984, Standal and Gjerde, 1987, Gjerde et al., 1994, Rye and Refstie, 1995) and are therefore suitable traits for improvement through genetic selection.
As the Atlantic salmon industry has expanded, meat quality traits have become of increased interest to producers. Flesh colour is considered to be an indicator of salmon freshness and quality and processors and retailers will downgrade or even reject product with insufficient colour (Nickell and Springate, 2001). The distinctive pink–red colour of salmonids is caused by carotenoid pigments in their diet. In current culture situations, pigments are usually added to feed in the form of astaxanthin (the most common form; Nickell and Springate, 2001) and canthaxanthin. These pigments are an expensive component of salmonid feeds so, to minimize costs, producers want animals that most efficiently absorb and retain these pigments in the flesh. Flesh carotenoid pigment content has thus also become a trait of interest for breeding programs. Family differences in flesh carotenoid pigment content have been observed in rainbow trout (Torrissen and Naevdal, 1984) and genetic parameters of carotenoid pigment contents were estimated in coho salmon fed a canthaxanthin-supplemented diet (Iwamoto et al., 1990). Flesh carotenoid pigment content genetic parameters have not been estimated in Atlantic salmon. Another carcass quality trait of increasing interest is flesh fat content because excessive fat content may have a detrimental effect on meat texture and also affect further processing; Gjedrem (1997) suggested that fat levels over 18% are too high. Genetic parameters of flesh colour and fat content have been previously estimated in Atlantic salmon (Gjerde and Gjedrem, 1984, Rye and Gjerde, 1996), coho salmon (Iwamoto et al., 1990, Neira et al., 2004), and rainbow trout (Gjerde and Schaeffer, 1989).
In the present study, data were collected on harvest body weight from four ASBDP year classes. Carcass quality parameters were also measured in one year class. The objective was to estimate heritability and genetic and phenotypic correlations among harvest weight and five carcass quality traits: colour score, flesh contents of carotenoid pigments astaxanthin and canthaxanthin, fat, and moisture. These genetic parameters should help predict how the ASBDP stock will respond to various selection techniques.
Section snippets
Family structures and husbandry
The ASBDP began in 1998 as a continuation of the Salmon Genetic Research Program (SGRP) and four separate SGRP lines of Atlantic salmon formed the basis of the ASBDP population. Fertilisation of four-year classes of salmon occurred in 1996, 1997, 1998 and 1999. In all year classes, random single-pair matings were done in November between four-year-old males and females to produce full-sib families. One strain within each year class was descended from separate strains produced by the SGRP (for
Trait heritability
Harvest body weights showed low to moderate heritability estimates ranging from 0.1 to 0.2 over all year classes (Table 2). These estimates were somewhat lower than heritability estimates found in other studies, which generally average 0.2–0.3 for Atlantic salmon 2–3 years of age (Gunnes and Gjedrem, 1978, Gjerde and Gjedrem, 1984, Standal and Gjerde, 1987, Gjerde et al., 1994, Rye and Refstie, 1995).
Colour score had slightly lower heritability than body weight, at about 0.14 (Table 2). This
Conclusions
Many Atlantic salmon traits are economically important to aquaculture and the ASBDP aims to create a strain with an optimal combination of fast growth rate, good flesh quality, and low incidence of early sexual maturation. The current study indicates that direct selection for weight in the ASBDP stock will have favourable indirect responses of higher colour scores and pigmentation but also an undesirable increase in flesh fat content. Future studies will examine the economic values of these
Acknowledgements
The authors would like to acknowledge the work and assistance of staff from the ASBDP and Skretting Canada (formerly Moore-Clark), Dr. L. R. McKay, Dr. L. R. Schaeffer, and the following companies: Aqua Fish Farms Ltd., Cooke Aquaculture Ltd., Harbour de Loutre Products Ltd., Heritage Salmon Ltd., Jail Island Aquaculture Ltd., and Stolt Sea Farms Inc.
References (19)
- et al.
Applications of selection for multiple traits in cage-reared Atlantic salmon (Salmo salar)
Aquaculture
(1995) - et al.
Estimates of phenotypic and genetic parameters for carcass traits in Atlantic salmon and rainbow trout
Aquaculture
(1984) - et al.
Body traits in rainbow trout: II. Estimates of heritabilities and of phenotypic and genetic correlations
Aquaculture
(1989) - et al.
Estimates of genetic and phenotypic parameters for body weight, growth rate, and sexual maturity in Atlantic salmon
Livestock Production Science
(1994) - et al.
Selection experiments with salmon: IV. Growth of Atlantic salmon during two years in the sea
Aquaculture
(1978) - et al.
Heritability and genetic correlations for flesh coloration in pen-reared coho salmon
Aquaculture
(1990) - et al.
Studies on carcass quality traits in two populations of Coho salmon (Oncorhynchus kisutch): phenotypic and genetic parameters
Aquaculture
(2004) - et al.
Responses to two generations of index selection in Atlantic salmon (Salmo salar)
Aquaculture
(1999) - et al.
Genetic variation in survival of Atlantic salmon during the sea-ranching period
Aquaculture
(1987)