Temperature, Development and Sexual Differentiation in Steelhead (Oncorhynchus mykiss)

Pacific salmonids (Oncorhynchus spp.) are genetic gonochores, but temperature during embryonic development might alter the phenotypic expression of the sex for salmon reared under controlled temperatures in hatcheries, or for wild fish subjected to climatic change. We reared steelhead from both wild and hatchery parents at three different temperatures (ambient, chilled 5^o below ambient and heated 5^o above ambient). We predicted that fish reared at ambient or chilled temperatures would not change sex during development. However, we predicted that a significant proportion of genetic females reared at the heated temperature would develop as phenotypic males. We predicted that source of the fish (wild, hatchery) would not affect sexual development or differentiation. At the conclusion of the experiment we measured fish for length and wet mass, determined genetic sex by examination of caudal fin clips and determined phenotypic sex from histological examination of gonads with light microscopy. We found no evidence of sex change for any fish in our study. The genetic and phenotypic sex of fish reared at all three temperatures showed complete concordance, and there was no effect of source (wild, hatchery) on sexual development.