Effects of temperature on gonadal sex determination in barfin flounder Verasper moseri

Temperature-dependent sex determination has been demonstrated in several species of fish. This study analyzes this phenomenon in barfin flounder Verasper moseri. The sex ratio was 1:1 when fish were maintained at 14 degrees C from Day 34 to Day 95. However, acclimation to 18 degrees C for 62 days resulted in an all male population. The proportion of males from 10.1 mm up to 29.7 mm in total length was affected by high temperature treatments. Survival rates were not affected by these treatments. Morphological differentiation of the gonad into either ovary or testis became distinguishable at 35 mm in total length. This time corresponds to the end of the temperature-sensitive period. These results suggest that gonadal sex was determined by temperature prior to the onset of gonadal sex differentiation in this fish.