Development of a selection index to improve market value of cultured Atlantic salmon (Salmo salar).

Genetic parameters were estimated on growth and development traits using analyses of variance and covariance of 42 full-sib families from a select line, 39 full-sib families from a control line of the same strain, and 37 full-sib families from another unselected strain. The traits included percent 1+ smolts, percent sexually immature fish after 1 year in seawater (nongrilse), and fork length measured at intervals throughout the production cycle. The number of fish sampled per family was 30 of 300-1500 for all freshwater traits and 15-60, i.e., all individuals present, for all seawater traits. Heritability estimates of freshwater traits had a broad range (0.15-0.61), but estimates were lower for seawater traits (0.06-0.29). There was a general reduction in heritability estimates for traits measured at increasing ages both in freshwater and seawater. These reductions may in part represent declines of maternal and common environmental effects that inflate heritability estimated from full-sib families. The genetic correlations indicated positive associations between freshwater and seawater growth parameters. However, the correlations decreased with increasing intervals between measurements. A selection index was developed using the estimates of the genetic and phenotypic parameters for three economically important traits: percent 1 + smolts, percent nongrilse, and harvest length. The seawater traits, percent nongrilse, and fork length at 17 months (harvest length) were the most important in the index.