Collapse of one-locus two-allele sex determining system by releasing sex-reversed hatchery fish

Sex determination in many fish species can be influenced by environmental variables such as temperature, salinity, and/or pH. For example, Japanese flounder (Paralichthys olivaceus) has male heterogametic sex determination (XX female and XY male), but XX juveniles can develop to become functional males depending upon environmental conditions. When environmental variables reverse a genetically determined sex, it is called sex reversal. If such a species is involved in a stocking program, the sex reversal can occur in the hatchery-reared stock, and there is a risk that the gene for sex determination may be exterminated. We have evaluated the conditions for the extermination of the sex determination gene for Japanese flounder and discussed how we can reduce such a risk. In this article, we extend the analysis to more general situations with both one-locus two-allele and environmental sex determination. Consequently, we generalize the result of the previous paper and conclude that using wild individuals as parent fish for stock enhancement (i.e., as broodstock) would be effective in reducing the genetic risk of stocking fish subject to environmentally influenced sex determination.