GENETIC AND ENVIRONMENTAL VARIATION OF FEMALE REPRODUCTIVE TRAITS IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

The variation and covariation of reproductive traits were studied by a nalyzing 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 sel ection experiment with rainbow trout conducted at Davis, California. V ariance components were estimated from a single trait animal model and covariance components from a two-trait animal model by using a deriva tive-free restricted maximum likelihood algorithm. Pooled over the thr ee 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 weig ht but small for other traits. Genetic correlations were estimated fro m data pooled over the three lines. Spawning date had significant gene tic correlations with spawning body weight, egg size and egg volume (0 .51-0.73) as well as with egg number (0.25). Significant genetic corre lations were also found for spawning body weight with egg size, egg nu mber and egg volume (0.47-0.67); and for egg size with fertility-hatch ability (0.35). As expected, the genetic correlations between egg numb er 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 origi nating from commonality among biological components and methods of mea suring these traits. The estimated genetic correlations between spawni ng body weight and egg production traits (egg size, egg number and egg volume) were positive, so that direct selection for growth rate or eg g production traits-should result in favorable correlated responses. T he low heritability of body weight, the moderately high heritability o f egg volume, and the strong genetic correlation between spawning body weight and egg volume, suggest that combined selection for body weigh t and egg volume could be an effective alternative selection method fo r improving growth rate and also reproductive capacity in rainbow trou t. (C) 1997 Elsevier Science B.V.