| As fish was lower vertebrates, it’s sex differentiation was effected by genetic and environmental factors(temperature, salinity, p H, population density, etc.), and temperature was the most important factor,also was the most attention research factor in recent years. Yellow catfish(Pseudobagrus fulvidraco Richardson) was incubated and cultivated at different water temperature to investigate gonadal differentiation and hormones(E2, T) levels of yellow catfish under different water temperatures.At the same time,we studied effect of different water temperature on growth rate of yellow catfish.Research results not only enriched scientific data of fish gonads differentiation and temperature on sex differentiation and so on, but also provided certain reference for development of yellow catfish unisexual control technology research.The results showed:(1).The histological differentiation occurred firstly in 15 days post hatching(dph) at(27±1)℃. There were two types of primordial gonad and one with cavitywill develop into ovary,and the other one without cavity will develop into testis. Ovarian cavity appeared first 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 themale. Gonads of the larva which reared under higher water temperature(32±1℃) differentiated earlier than those under middle temperature(27±1)℃about 5-10 days. Gonads under lower water temperature(32±1℃) differentiatedlater thanthe larva under middle temperature(27±1℃)about 25-30 days.(2). Incubated and cultivated at middle water temperature(27±1)℃ and lower water temperature(22±1℃), the sex ratio was close to 1:1(1:0.96 and 1∶1.17 respectively). However, Incubated and cultivated at higher water temperature(32±1)℃, the sex ratio was 1∶2.10, and proportion of males were(67.70±0.54)%(p < 0.05). Zygote of yellow catfish incubated at temperature of(32±1℃),and continuous cultivated at temperature of(32±1℃) for 7 days, could significantly improve the proportion of male.This result showed that temperature can influence gonad differentiation of P. fulvidraco and higher water temperature(32±1℃) can induce masculination.(3). As the yellow catfish gonad development,the level of estradiol(E2) showed a rise first followed by a decline under different water temperature.E2 levels reached maximum at 14 days past hatch under temperature of(27±1℃),(32±1℃),(34±1℃).(27±1℃) group and natural water temperature incubation group reached the maximum at 7 dph. E2 levels of yellow catfish had no significant difference(P > 0.05).between different water temperature at 7 dph. In(32±1℃) group,(34±1℃) group,E2 levels were significantly higher than in(22±1℃) group,(27±1℃) and natural water temperature(25~27℃) incubation group at 14 dph. E2 levels of(32±1℃) group was significantly lower than the rest of group at 60 dph. At 3 dph, testosterone levels at different water temperature had no significant difference(p > 0.05), but then there were certain differences between groups after a period of time. In(27±1℃) group and(32±1℃) group,T levels were significantly lower than in(34±1℃) and natural water temperature(25~27℃) incubation group at 7 dph. T levels in(27±1℃) group was(0.16±0.03ng/g),and significantly lower than other groups at 14 dph. T levels in(26±1℃) group was(9.57±0.29ng/g),and significantly higher than other groups at 60 dph(P < 0.05).(4). There were significant difference in growth rate of Pseudobagrus fulvidraco(Richardson) under different water temperature in early stage(3-60d). The RL, RW,SGR of yellow catfish under water temperature was significant difference(p < 0.05).The relationship equation between RL, RW,SGR and water temperature was RL=-1.02×10-3T2+5.93×10-2T-7.42×10-1(R2=0.9984),Rw=-12.9T2+749T-1.00×104(R2=0.981),RL=-4.99×10-4T2+2.91×10-2T-3.17×101(R2=0.9926),respectively.Yellow catfish would get the best RL, RW,SGR when water temperature was 29.69℃、28.96℃、29.16℃,respectively. |
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