Genetic and environmental variation of female reproductive traits in rainbow trout ( Oncorhynchus mykiss)

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The variation and covariation of reproductive traits were studied by analyzing data from 2020 females divided into 377 full sib families and covering five generations of three lines—a random mated control line (C), an egg size (+) line (E) and a body weight (+) line (Y), in a selection experiment with rainbow trout conducted at Davis, California. Variance components were estimated from a single trait animal model and covariance components from a two-trait animal model by using a derivative-free restricted maximum likelihood algorithm. Pooled over the three lines, the estimates of heritability were 0.65 for spawning date, 0.14 for spawning body weight, 0.60 for egg size, 0.55 for egg number, 0.52 for egg volume and 0.13 for fertility-hatchability. The estimates in line C were lower for spawning date, spawning body weight and egg number, and higher for egg size and fertility-hatchability than those in line E and line Y. Full-sib family effects caused by factors other than additive genetic effects were considerable for spawning body weight but small for other traits. Genetic correlations were estimated from data pooled over the three lines. Spawning date had significant genetic correlations with spawning body weight, egg size and egg volume (0.51–0.73) as well as with egg number (0.25). Significant genetic correlations were also found for spawning body weight with egg size, egg number and egg volume (0.47–0.67); and for egg size with fertility-hatchability (0.35). As expected, the genetic correlations between egg number and egg volume and between egg size and egg volume (0.81 and 0.48) were strong and significant due to the partial auto-correlations originating from commonality among biological components and methods of measuring these traits. The estimated genetic correlations between spawning body weight and egg production traits (egg size, egg number and egg volume) were positive, so that direct selection for growth rate or egg production traits should result in favorable correlated responses. The low heritability of body weight, the moderately high heritability of egg volume, and the strong genetic correlation between spawning body weight and egg volume, suggest that combined selection for body weight and egg volume could be an effective alternative selection method for improving growth rate and also reproductive capacity in rainbow trout.