Comparative Study on Hatching Rate, Survival Rate, and Feminization of Onychostoma barbatulum (Pellegrin, 1908) at Different Temperatures and Examining Sex Change by Gonad and Karyotype Analyses.

Mei-Chen Tseng, Dian-Hao Yang, and Tsair-Bor Yen (2017) Onychostoma barbatulum has become an aquaculture species with high economic value in Taiwan. It was observed that females can grow faster to a larger size than males on aquaculture farms. Therefore, development of feminized fry can increase farm profits in the future. The purpose of this study was to establish the optimal incubation, feed, and feminization temperatures to produce a high feminization ratio and better survival rates for O. barbatulum fry. The performance mode of sex-determination by temperature was also explored in the study. Adults were collected from Nanzixian Stream in southwestern Taiwan and artificially propagated in tanks. Fertilized eggs were placed in environments of different temperatures to determine the hatching rate (n = 3000) and the survival rate (n = 3000) of fry. After 6 months, the sex ratio was established from gonad tableting (n = 360). A karyotype analysis (n = 86) was also conducted to verify the existence of gender-reversed individuals. The results showed that hatching rates at 17.5, 19.5, 21.5, 23.5, and 25.5°C were 70.7%, 67.3%, 73.3%, 33.7%, and 34.7%, respectively. Survival ratios from low to high temperatures were 34.7%, 47.7%, 33.7%, 12.3%, and 23.3%, respectively. These results indicated that both the hatching rates and survival ratios of fry performed poorly at temperatures higher than 21.5°C. The performance mode of sex-determination by temperature of O. barbatulum revealed that female ratios significantly decreased at the two extremes of the temperature range, while the female ratio was highest at an intermediate temperature. The best feminized ratio (83.4%) was observed at 21.5°C among all tested temperatures (p < 0.05). Meanwhile according to a karyotype analysis, sex-reversed individuals were found in each group, indicating that temperature is a critical phenotypic sex-determining factor. Therefore, rearing O. barbatulum fry at a proper water temperature can effectively increase the female sex ratio and maintain high hatchability and survival ratios. These results can potentially be applied to produce a high proportion of female fry on aquaculture farms.