Artificially induced sex-reversal and gynogenesis in darkbarbel catfish (Pelteobagrus vachelli)

Pelteobagrus vachelli and hybrid yellow catfish (P. vachelli♂×P. fulvidraco♀) exhibit significantly sexual dimorphism in growth. In order to obtain monosex populations of P. vachelli and hybrid catfish with better growth performances, we performed the study on sex control technology and gynogenesis to obtain the YY super-male P. vachelli. Firstly, different dosages of estradiol valerate (EV) and 17β-estradiol (E₂), and a range of treatment periods of E₂ were explored on the gonadal differentiation, growth and survival rate of P. vachelli. Then, the sex-reversed fish were used to identify the best condition for gynogenesis. The results showed that lower EV (5 and 10 mg/kg) treatment led to an incomplete sex reversal in P. vachelli during 7-60 day-post hatching (dph). In contrast, 20 and 40 mg/k E₂ treatment led to complete feminization, while the body length, body weight and survival rate of E₂-treated fish were significantly higher than of the EV-treated fish. The feminization rate of P. vachelli treated with 20 mg/kg E₂ was 100% during the period of 22-40 dph, and in which the growth performance and survival rate were close to that of the control group. Furthermore, cytological observation showed that the separation of the second polar body from female pronucleus of fertilized egg occurred as early as at 6 min post-fertilization under 25 °C. We optimized the condition for gynogenesis by applying cold shock at 4 °C for 20 min on eggs at 6 min post-fertilization. A total of 62 gynogenetic fish were identified by a pair of genetic markers that could efficiently distinguish yellow catfish, darkbarbel catfish and their interspecific hybrid, of which 10 gynogenetic fish were sacrificed and 3 fish were males. It was inferred that they were YY super-males. Our results indicated that E₂ treatment could efficiently induce feminization of P. vachelli, and YY super-male can be obtained by gynogenesis of the feminized P. vachell, which lays the foundation for the variety improvement and cultivation of all-male P. vachelli and all-male hybrid catfish (P. vachelli, ♂×P. fulvidraco, ♀).