Individual growth rate and age at sexual maturity in rainbow trout

Abstract

Growth rate possible connection between growth rate and age at sexual maturity were studied on individually tagged rainbow trout from different sib groups. Considerable variation in growth rate and age at first sexual maturity was found among sib groups. Significant correlations were found between size (length) of the individual fish and group mean, measured at different times during the sea phase. The mean lengths within groups of fish maturing during their third year were significantly higher than for fish still immature in the autumn preceding spawning, as well as half a year before and even one year before spawning. The relationship between sex and size of the fish was not clear, but in some groups the males were on average larger than the females. Fish maturing during their second year (mostly males) showed nearly the same mean size as immature fish of the same age before the spawing season. They grew considerably less during the spawing season, and showed somewhat increased mortality rate, but during the next summer they matured again and showed greater relative growth rate than the other fish.