Gonadal differentiation and temperature effects on sex determination in the freshwater pike silverside Chirostoma estor Jordan 1880

The gonadal description of the freshwater atherinopsid pike silverside Chirostoma estor suggests that the gonads differentiate as ovaries or testes by 8 weeks after hatching when raised at 21 A degrees C. Thermal treatments at 14 A degrees C, 21 A degrees C and 29 A degrees C applied from fertilisation, clearly affected phenotypic sex ratios, suggesting that the thermolabile window of sex determination occurred early in development. In this study, exposure to the highest temperature led to male-biased sex ratios in this species. However, the effects of the lower and medium temperatures on the sex ratios were less clear, suggesting the presence of a mixture of genotypic and temperature-dependent sex determination (TSD) mechanisms in C. estor, similar to other atherinopsids. This work further enhances our knowledge regarding the diversity and plasticity of TSD mechanisms in atherinopsid and teleost fish.