Objective  Water temperature required to induce feminization on male channel catfish fries before sex differentiation was determined.

  Method   One-dah channel catfish fries were treated for 30 d in water at the temperature of (30±0.5) ℃ (T-30, CK), (33±0.5) ℃ (T-33) or (36±0.5) ℃ (T-36). Growth and rates of survival, ovarian formation, and sex reversal of individual fish that had ovaries differentiated and formed in 60 d with positive genetic sex identification were measured, calculated, and recorded. In each group, the ovarian development of XX and XY females as determined by the anatomy and H&E staining sections was compared and analyzed. Subsequently, qRT-PCR was used to detect the expressions of foxl2 and dmrt1 in XX and XY female ovaries as well as XY male testis at 150 dahs.

  Result   The survival rates of the fries under T-30, T-33, and T-36 were 95.33%, 91.33%, and 82.67%, respectively. The body length of the fish under T-30 measured at 9.13 cm, under T-33 at 10.14 cm, and under T-36 at 8.80 cm, while the body weighed at 6.31 g for CK, 9.76 g for those under T-33, and at 6.11 g for those under T-36. The ovarian formation percentages were 51.00% under CK, 66.67% under T-33, and 77.67% under T-36. On sex reversal, the majority of oocytes in the XX females were at stage Ⅱ under T-30, but under T-33 and T-36 in the XY females. The stage Ⅲ oocytes were found in the XX females under T-30 as well as in the XY females under T-36. Under T-33, the XY female channel catfish showed slow oval development with unclear outline and coelomic mucosa. The expression of foxl2 was upregulated and that of dmrt1 downregulated in the XY females.

  Conclusion  The physiological sex before sexual differentiation of channel catfish could be converted to female by continuous high-temperature induction.