Gonadal differentiation of yellow catfish (Pseudobagrus fulvidraco Richardson) under different water temperatures was investigated by histological sectioning,and the effects of different temperatures on sex determination were studied.The results showed that the histological differentiation of yellow catfish occurred firstly at 15 days post hatching (dph) under (27±1)℃.There were two types of primordial gonad and one with cavity will develop into ovary,and the other one without cavity will develop into testis.Ovarian cavity firstly appeared at 15 dpt (the total length reached 13.99±0.24 mm) and the occurrence of spermaduct and seminiferous lobule began at 60 dpt (the total length reached 47.58±1.74 mm).This experiment showed that germ cell division in the female was earlier than that in the male.Gonads of the larva reared under higher water temperature (32±1)℃ differentiated about 5-10 days earlier than those under moderate temperature (27±1)℃.Gonads under lower water temperature (32±1)℃ differentiated about 25-30 days later than the larva under moderate temperature (27±1)℃.The sex ratio under moderate or lower water temperature was close to 1∶1 (1∶0.96 and 1∶1.17 respectively).However,the sex ratio under higher water temperature was 1:2.10,and the proportion of males were 67.70%±0.54% (P<0.05).This result suggested that temperature can influence gonad differentiation of P.fulvidraco and higher water temperature (32±1)℃ can induce masculination.