Effects Of Sex Steroid Hormones And Temperature On Sex Differentiation Of Clarias Fuscus

Clarias fuscus, a kind of important commercial freshwater fish in China, which characterized byits delicate, strong adaptability, and high nutrition, were selected as our experimental animal. FemaleC. fuscus has heavier ovaries, which results in lower price than that of males. Because of that, a high-er propotion or whole males fries were required for the more economic benefits. Time of sexdifferentiation, as well as the occurrence and differentiation of gonad in C. fuscus was studied bymorphologic observation and histological sections. In addition, effects of17α-methyltestosterone（17α-MT）,17β-estradiol （17β-E₂） and temperatures （24°C,28°C, and32°C） on growth, survivalrate, sex ratio, gonad histology and Foxl2expressions in C. fuscus were examined. Main results asfollows:1.Studies of sex differentiation in C. fuscusThe early morphological characteristics of gonad between males and females C. fuscus weredifferent distinctly. Rapidly proliferating, pear-shaped gonads would become ovaries, while lightlyproliferating, fusiform gonads would become testis in the future. In addition, sex differentiation timeof females was earlier significantly than that of males. The sign for ovaries differentiation was theemergence of the ovarian cavity on day16, and that of the testis differentiation was the formation ofspermatic ducts&lobules on day30, respectively at26±1℃. Oogonia proliferated rapidly bymitosis on day18, and then developed into the maturation stage on day22in female C. fuscus.However, spermatogonia proliferated rapidly on day30, but developed into the maturation stage onday40in male C. fuscus.2. Efeccts of17α-MT on growth and sex differentiation in C. fuscusTwo-day juvenile C. fuscus were immersed in different doses of17α-MT （50,100, and200μg/L）for30days. Results showed that17α-MT at dose of200μg/L had no influence on suvival rate butinhibited the growth in C. fuscus; howeve, dose of50and100μg/L17α-MT had no influence on bothsuvival rate and growth. Doses of100and200μg/L17α-MT produced more males （70%and76%,respectively） than50μg/L17α-MT （54%） did （P<0.05）, but no significant difference in sex ratio wasobserved between the50μg/L17α-MT treated group and the control group （56%）. Dose of100and200μg/L17α-MT accelerated the occurrence of primary spermatocytes for3and5days, but deferredthat of ovarian cavity for4and6days, and primary oocytes for8and9days, respectively.17α-MT doses from100to200μg/L delayed the ovarian but accelerated the spermatic development, and doseof200μg/L17α-MT inhibited the expression of foxl2.3. Efeccts of17β-E₂on growth and sex differentiation in C. fuscusTwo-day juvenile C. fuscus were fed in different doses of17β-E₂（100,200, and300μg/g） for30days. Results showed that17β-E₂at dose of300μg/g had no influence on suvival rate but inhibitedthe growth in C. fuscus; howeve, dose of100and200μg/g17β-E₂had no influence on both suvivalrate and growth.Doses of200and300μg/g17β-E₂produced more males （74%and78%, respectively）than the control group（P<0.05）, but no significant difference in sex ratio was observed between the100μg/g17β-E₂treated group （66%） and the control group （56%）. Dose of200and300μg/g17β-E₂accelerated the occurrence of ovarian cavity for2and3days, and primary oocytes for1and3days, respectively, but deferred that of primary spermatocytes for3and7days.17β-E₂doses from200to300μg/g delayed spermatic but accelerated the ovarian development, and dose of300μg/g17β-E₂increased the expression of foxl2.4. Efeccts of temperature on growth and sex differentiation in C. fuscusTwo-day juvenile C. fuscus were reared at24℃,28℃and32℃for30days. Results showedthat the faster growth and the lower survival rate were observed in the32℃group than in the24and28℃group （P<0.05）, while24and28℃group had no significant difference in growth and survivalrate. Significant high males were found in28and32℃group （66%and80%,respectively） than in24℃（55%） and the control group （P<0.05）. High temperature （32℃） accelerated the thedevelopment of gonad, and the ovarian cavity, primary oocytes and primary spermatocytes occurredat least2days early.