Production of YY super-males in Pseudobagrus ussuriensis using estradiol-induced XY pseudo-females

The Ussuri catfish Pseudobagrus ussuriensis belongs to the XY sex-determination system of male heterogamy, exhibiting typical male-biased dimorphism during growth and development. Therefore, all-male breeding possesses substantial economic significance. It is fundamental to all-male breeding to obtain XY pseudo-female and YY super-male fish. In this study, fry (6 days post-hatching, 2-3 mm total body length) were treated with 17-β estradiol, at graded doses of 50, 100, 150, and 200 µg/L for 40 days to induce sex reversal. After treatment, XY pseudo-females were screened using male-specific molecular markers. Upon reaching sexual maturity, XY pseudo-females were mated with XY males by artificial insemination. After 1 year of rearing, YY super-males were identified from a mixed filial population. Subsequently, gonadal histological examination of XY pseudo-females and YY super-males was conducted. The results indicated that XY pseudo-females were produced across all four E2 concentrations. Higher rates of sex reversal and survival could be achieved under the treatment of 150 µg/L E₂. The absolute and relative fecundity of XY pseudo-female fish were not significantly different from those of XX female fish. The proportion of YY super-male fish ranged between 9.32 and 16.59%, which was considerably lower than 25%. Mating experiments and histological examination of gonads indicated that XY pseudo-females and YY super-males were viable and fertile. In conclusion, this study demonstrates the breeding of all-male Ussuri catfish to produce YY super-male fish, adding a new strain to enhance the aquaculture production.