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 (M_YY) requires a better understanding of reproductive performance. We measured the reproductive performance of hatchery age-0 and age-1 M_YY brook trout compared to hatchery XY males using laboratory crosses. Offspring of XY males had higher survival than offspring of age-1 M_YY 1-day post-fertilization, but not offspring of age-0 M_YY . 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 M_YY were 3.6% smaller in length and 25.2% smaller in weight than those of XY males. For crosses fertilized by both M_YY and XY males, we found that a significantly higher proportion of offspring within families were sired by M_YY versus XY males. These results show, under controlled conditions, evidence for possible fitness advantage for M_YY under sperm competition, but a possible fitness disadvantage associated with early growth of their offspring. Overall, our results hold promise for the use of M_YY brook trout to serve as an effective eradication tool.