Effects of temperature on sexual development in steelhead, Oncorhynchus mykiss

We evaluated how genotype (stock source, parental line, chromosomal sex) and temperature interact to influence gonad development and phenotypic sex of Oncorhynchus mykiss. Embryos were generated from single pair matings of natural-origin and first-generation hatchery-origin O. mykiss held at ambient or elevated (5 °C above ambient) water temperature. Exposure to elevated temperature lasted from fertilization until the onset of exogenous feeding, after which all experimental groups were maintained at ambient temperature. Sexual phenotype was determined by histology and sexual genotype by the OmyY1 marker. There was 99% concordance among fish sexed both phenotypically and genotypically, demonstrating that experimental factors, including elevated rearing temperatures, did not result in sex change. Approximately 10% of the histologically examined fish showed no evidence of gonad development beyond the indifferent stage. Most of these fish were from hatchery family lines.