An initial description of the quantitative genetics of growth and reproduction in the mosquitofish, Gambusia affinis

Abstract

Three stocks of mosquitofish were reared under identical conditions through one complete life cycle to quantify phenotypic and genetic variability for traits of growth and reproduction. At 60 days of age females and males averaged 473 mg and 183 mg in weight and 26.2 mm and 20.9 mm in length, respectively. Significant differences were found among stocks for both sexes in both traits. Rearing density strongly affected female size; its effection male size was much less pronounced. Stage of maturity and male size were closely related, with maturing males being significantly larger than either mature or very immature fish. Heritability estimates for males were 0.25 for both length and weight, for females 0.72 for length and 0.77 for weight. Males averaged 55 days of age at sexual maturity. There were no significant differences among stocks, nor was there a significant effect of density on this trait. Heritability of age at maturity was estimated to be 0.41. Maturation of the first male to mature in a tank appeared to be under much weaker genetic control than maturation of subsequent males, suggesting a genotype-environment interaction. The size of first broods of virgin females averaged 23 fish. Significant differences between stocks for size of first brood were apparent only when female weight was considered. Heritability of brood size was estimated to be 0.16 without correction for female weight, and was impossible to estimate but presumably very low when corrections were made for female weight. Although female weight significantly affected brood size, it accounted for only 13% of the variation in the trait.