Genetic Gain for Growth and Delayed Sexual Maturation Using a Feral Strain of Anadromous Brook Trout

A selective breeding program was initiated with a wild population of anadromous brook trout Salvelinus fontinalis from the Laval River, Quebec. The objective was to develop a new strain characterized by improved growth and reduced precocious sexual maturation. A control line was maintained by use of random within-family selection. Length and weight were measured and sexual maturity (mature or not mature) was determined at the end of the second year of growth (22 months of age). In the selected line, phenotypic variance, additive genetic variance, and heritability for weight within the selected families were reduced. A comparison between generations showed that fish weight at 22 months in the selected line increased by 23.1% from the F1 to the F2 generation and by 32.1% from the F2 to the F3 generation. The control line increased similarly in weight from the F1 to the F2 generation (34.7%) but not thereafter; this result was probably due to the domestication effect in the first generation after captivity. The proportion of fish that were immature at 22 months was 32.2% in the F1 generation and increased to 61.4% by the F3 generation in the selected line; the proportion immature did not change significantly after two generations in the control line (27.5%). Our results show that simultaneous selection for growth and late sexual maturation are compatible goals for brook trout breeding programs.