Effects of Rearing Environment and Strain Combination on Heterosis in Brook Trout

Abstract

AbstractThree strains of brook trout Salvelinus fontinalis (domestic [D], Laval [L], and Rupert [R]) and their reciprocal hybrids were reared from 7 to 21 months of age in three different environments (indoor, constant temperature conditions; indoor, seasonal temperature variations; and outdoor, seasonal temperature variations) to test for the occurrence of heterosis in important life history traits of interest for production (body mass, length, condition factor, the absence of early sexual maturation, and survival). For each cross, body mass, length, and mortality were measured at regular intervals and sexual maturity was assessed in age‐1+ fish (21 months of age). We found evidence for heterosis in mass and length that varied according to strain, cross direction in reciprocal hybrids, developmental stage, or environment; no significant outbreeding depression was detected for these traits. Heterosis expression for weight varied from 4.9% to 23.8% depending on the hybrids and environments. We found that one out of five reciprocal hybrids tested (L[female]R[male]) expressed heterosis at each age stage throughout the experiment in the three environments while the other four had mixed results. No evidence for heterosis was observed for sexual maturity and survival. These results not only provide one of the first clear pieces of evidence for the occurrence of heterosis in salmonids but also illustrate the complex nature and the unpredictability of this phenomenon.