Effects of size and spring growth on sexual maturation in 1+ Atlantic salmon (Salmo salar) male parr: interactions with smoltification

Individually identified 1-year-old Atlantic salmon (Salmo salar) parr of Baltic origin were subjected to four different restricted feeding regimes during May and June, and the effects of feeding regime and fish length on the probability of sexual maturation in males were evaluated using logistic regression. Food restriction in June decreased specific growth in weight during June to ca. 22% of that in the control. On average, the maturation rate was reduced from 60% in controls to 48, 45, and 36% in groups on restricted rations. Furthermore, the positive effect of initial length on the probability of maturation was depressed in groups on restricted food in June or May and June. The results of this study show that food restriction in spring has a significant negative effect on the probability of maturation in male salmon parr, but maturation seems to be suppressed in only a small part of the experimental populations. The occurrence of maturing males among fish with a very low or negative growth rate during June and poor condition by the end of June implies, however, that high growth rate in June is not necessary for the onset of rapid gonadal growth in early summer.