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Zexia Gao, OSU South Centers
Hanping Wang, Co-Researcher
Geoff K. Wallat, Co-Researcher
Jacob D. Rapp, Co-Researcher
Paul O-Bryant, Co-Researcher
Hong Yao, Co-Researcher
Laura G. Tiu, Co-Researcher
Zexia Gao, Female, Chinese, PhD student in Joint Training Program between Ohio State University (OSU) and Huazhong Agriculture University (HZAU) in China, majoring in Fish Physiology and Genetics.
Investigation of polyploidy status of loaches in China;
Physiology and biochemistry of fish peripheral blood;
Functions of primordial germ cells in sex differentiation in fish;
Sex determination mechanism in bluegill.
Bluegill sunfish Lepomis macrochirus have become an increasing-economically important fish. Hayward and Wang (2006) found the inherent growth rate of bluegill males was twice that of females, and males could reach commercial size (250g) in eight months from juvenile. Therefore, developing a process for mass-production of genetically male bluegill populations via genetic manipulation is very important. In the case of heterogametic male mode (XY), crosses between feminized XY males and regular XY males are expected to yield approximately 75% males. Estradiol-17b (E2) has been recognized as the most preferred hormone to get the feminized XY males. Special attention is given to the dose, timing and duration of treatment. The objectives of our present study were to evaluate the effectiveness of various estradiol-17b treatments on the growth performance, production and gonadal structure of sex-reversed female bluegill at both sex-ratio and histological level through bluegill breeding program.
Natural spawning method was applied without using hormones. When fry were four weeks of age, fish received E2 at the doses of 50, 100, 150 and 200 mg/kg feed 3 times daily for 60 days. The control and experimental groups made a total of five groups, each having four replicates. 15-30 samples in each group were sexed at the age of 15 months. Feed consumption (FC), growth and mortality were monitored to determine the E2 consumption (E2C), and growth during and after treatment.
Results indicated that the survival of fish increased as E2 dosage decreased, while there were no significant differences being detected among treatments. All the E2 treated groups were effective and produced 100% monosex female populations from a 66.1% female experimental population. FC of fish in 100, 150, 200 mg/kg E2 treatments were significantly higher than that in control group. E2 had negative effects on growth rate during the period of treatment, while there was no side effect detected after the treatment. In summary, this study demonstrated that in bluegill it is successful to influence sex differentiation in favor of females by oral administration of E2. Moreover, considering all the effect of estradiol-17b on its survival, growth during and after E2 treatment, sex ratio, we concluded that the E2 dose of 150 mg/ kg was the best optimal dosage for feminization in bluegill, with 50 and 100 mg/ kg being sub-optimal and 200 mg/ kg over-optimal.