Résumé
The rainbow trout is the most widely farmed freshwater species in Europe. Early research on the genetic basis of egg production began in the 1970s, but with several generations of selective breeding now established—mainly focused on body weight—understanding the genetic relationships between growth and spawning performance has become necessary. This study investigated a commercial line of rainbow trout, monitoring about 1600 females from 656 families, from portion size (355 g) to maturity (2600 g), to assess egg production traits at first spawn (total spawn weight and egg number, mean egg weight, relative fecundity, and gonado-somatic index). Thermal growth coefficients (TGCs) were calculated across six periods until spawning. Fillet fat content was measured, and carcass yield was predicted non-invasively through ultrasound tomography. Heritabilities and genetic correlations between growth, carcass quality and spawning traits were estimated using linear animal models. Genetic correlations between body weight at different ages and spawning traits were either nonsignificant or positive (0.05 to 0.70). Comparable trends were observed for TGCs (-0.20 to 0.63) and carcass yield at 16 months (-0.03 to 0.24). In contrast, predicted carcass yield at 20 months showed negative genetic correlations with spawning traits (-0.16 to -0.47). These findings indicate that selection for growth up to 20 months should not adversely affect and may improve spawning performance. However, improving carcass yield after 20 months may compromise egg production. Monitoring spawning performance in selective breeding programs is advised to anticipate shifts in genetic correlations and to optimize selection strategies all along the life cycle.