Lab-based evaluation of the reproductive performance of Trojan (M_YY) brook trout (Salvelinus fontinalis)

Evaluating the efficacy of the use of Trojan male brook trout with two Y chromosomes (MYY) requires a better understanding of reproductive performance. We measured the reproductive performance of hatchery age-0 and age-1 MYY brook trout compared to hatchery XY males using laboratory crosses. Offspring of XY males had higher survival than offspring of age-1 MYY 1-day post-fertilization, but not offspring of age-0 MYY. We found no detectable differences in survival from eyed-egg to the juvenile-fry stage. However, size-at-age differed, where offspring of age-0 MYY were 3.6% smaller in length and 25.2% smaller in weight than those of XY males. For crosses fertilized by both MYY and XY males, we found that a significantly higher proportion of offspring within families were sired by MYY versus XY males. These results show, under controlled conditions, evidence for possible fitness advantage for MYY under sperm competition, but a possible fitness disadvantage associated with early growth of their offspring. Overall, our results hold promise for the use of MYY brook trout to serve as an effective eradication tool.