The genetics of age and weight at sexual maturity based on individually tagged rainbow trout ( Oncorhynchus mykiss)

Abstract

Age and body weight at sexual maturity are important traits for aquaculture as is the relationship between the traits. The genetics of rainbow trout age at maturity (days), an indication of the time of spawning within a season, and body weight at maturity were investigated for two consecutive spawning seasons. The relationship of the maturity traits to each other and to body weight at specific ages was evaluated. During the first spawning season, data were obtained on early maturing males (E-males), mature at an average of 301 days post-fertilization. During the second spawning season, data were collected on females, males mature for the first time (T-males), and males mature for the second time (E-males), mature at an average of 697, 685, and 673 days, respectively. Estimation of genetic parameters was accomplised using an additive genetic and maternal mixed model. Heritability estimates for age at maturity were high, 0.86 and 0.60 for the first and second seasons, respectively. The heritability estimate for body weight at maturity for the first season was also high, 0.89, but was a moderate 0.27 for the second season. For both spawning seasons, there appeared to be little genetic relationship between age at maturity and body weight measured approximately 0 and 2 months before the first mature fish was found. However, the genetic correlation between age at maturity in the second season and body weight measured on the day the last mature fish was found (740 days) was 0.56. The genetic correlations between age at maturity and body weight at maturity within the same season were 0.67 and 0.58 for the first and second seasons, respectively. For both seasons, genetic correlations between body weight at maturity and body weight measured at other specific ages were fairly high, ranging from 0.50 to 0.99. The genetic correlation between body weight at maturity for the first and second seasons was 0.51. Selection to genetically improve body weight from 0 to 2 months before the spawning season should not affect the timing of spawning. However, selection to decrease the age at maturity and alter the spawning season may affect body weight at maturity and thus characteristics of the eggs.