Abstract
A quantitative genetic analysis of body condition, body shape, skin colour and spottiness of large, farmed rainbow trout Oncorhynchus mykiss showed that the traits can be modified through selective breeding. This was indicated by their high heritabilities (h2 = 0·46–0·61 on the underlying liability scale and 0·29–0·50 on the observed scale). Correlations calculated using linear models showed that skin colour and the amount of spots displayed positive phenotypic (rP = 0·33) and genetic correlations (rA = 0·83), the relationship being advantageous for the genetic improvement of the traits. Body shape and condition factor displayed disadvantageous correlations with body mass at both ages, the genetic correlations between the traits ranging from 0·36 to 0·57. It was concluded that there are no strong genetic constraints for the genetic improvement of appearance, the only limitation being that rapidly growing fish become rotund.
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