Genetic parameters of growth in rainbow trout, Salmo gairdneri, prior to maturation

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Abstract
The relative magnitude of additive genetic effects, nonadditive genetic effects, maternal effects, and common environmental effects was determined for size, growth, and condition factor in rainbow trout of various ages, from the egg to the yearling stage, using a factorial mating system. Heritability estimates for length and weight ranged from 0.9 to 0.32, except for dried egg weight, where no additive genetic variation was detected. Condition factors were more heritable than size, with heritability estimates ranging from 0.24 to 0.46. Maternal effects were only important for dried egg weight and early fry size, and decreased rapidly with age as heritability increased. Egg weight, fry size, and fry condition factors were influenced by common environmental effects and (or) nonadditive genetic effects, but confounding of these sources of variation prevented exact estimation of their relative magnitude. Nonadditive genetic effects were completely absent for yearling size but were present for yearling condition factors. Individual or between-family selection on size should produce some response unless selection is done on very young fry or familis are housed separately. For very young fry or where families are not replicated across tanks, within-family selection will be nescessary to identify genetically superior fish, because of strong maternal or common environmental effects. Genetic correlations between size or condition factors measured at different ages were all positive, so selection at one stage should improve size or condition factor at another.