GODWIN, J.; LUCKENBACH, J.A.; BORSKI, R.J.: Temperature Influences on Sex Determination and Development in Flounder.

A variety of environmental factors can influence sex determination and sexual development in teleost fishes. These include temperature, pH, and social interactions. Evidence suggests a critical role for gonadal steroid hormones in sex determination and gonadal morphogenesis, but dependence of development of other aspects of the sexual phenotype on gonadal steroids appears evolutionarily more labile. Flounder species are proving useful models for examining temperature effects on sex determination and growth. Temperature affects sex determination in both Southern and Japanese flounder (Paralichthys lethostigma and P. olivaceus) and in the barfin flounder (Verasper moseri). In Paralichthys, these effects apparently only occur in the homogametic sex (XX individuals) with heterogametic individuals developing as males. The pattern of temperature effects in these species is similar to that described for some reptiles, with mid-range temperatures producing the highest proportions of females, while both higher and lower temperatures produce strongly male-biased sex ratios. Information is limited, but it also appears that temperature effects vary with latitude across flounder species, with the temperatures inducing female determination being cooler at higher latitudes. Interestingly, the temperature that promoted the fastest growth in males and females in our southern flounder experiments also produced the highest proportion of females. Since females attain larger body sizes in flounder, this finding may support the hypothesis that the temperature experienced during development has differential effects on fitness through effects on growth.