Histological characterization of gonadal development of juvenile Lake sturgeon (Acipenser fulvescens)

Lake Sturgeon ( Acipenser fulvescens ) hatcheries that produce juveniles to augment natural populations are of increasing importance to management and species recovery. Maintaining balanced sex ratios of juveniles that are released into the wild is important to future natural reproduction. Greater understanding of the chronology of gonadal development of hatchery-reared fish can help managers target ages to conduct surveys, predict cohort sex ratios, and maintain demographically healthy adult populations. We histologically characterized gonadal development of juvenile Lake Sturgeon between the ages of three to 53 months. Gonads of all surveyed fish ( N = 56) were undifferentiated and immature at all time-points surveyed until 41 months, although histological changes consistent with gonadal enlargement and development were observed (e.g., increase of adipose tissue, gonadal epithelial ridge thickening). At 41 months, sex could be determined in two (25%) of the eight sampled fish based on presence of ova within the gonadal tissue, and five (62.5%) showed continued gonadal development, but were still undifferentiated (sex could not be assigned). At 53 months, sex could be determined in six (75%) of eight sampled fish. Two (25%) showed advanced development (e.g., epithelial thickening of the germinal ridge), but the gonads were undifferentiated (i.e., no ova or spermatozoa present). Delayed gonadal differentiation is consistent with the delayed sexual maturity generally observed in Lake Sturgeon relative to other teleost species. Sample sizes precluded statistical evaluation, however, sex determination did not appear to be associated with egg incubation temperature.