The failure of male-typical SSCs and mating behaviors in the cyp17a1 KO fish was resolved by androgens supplementation. Gross appearances of the representative fish (A–E). The white boxes in (A) and (C) indicate the feminized anal fin coloration, whereas the black boxes in (B), (D) and (E) indicate the male-typical anal fin coloration. (F–J) BTs visualization of representative fish. The white arrows in (F) and (H) indicate the lack of the BTs in the pectoral fin, whereas the black arrows in (G), (I) and (J) indicate the area of BTs in the pectoral fin. (K–R) Mating behaviors monitoring of representative fish. Parallel swimming, grasping, and spawning were observed in the control males with WT females, and cyp17a1 KO male zebrafish after T and 11-KT treatment with WT females. Opposite swimming and encountering could only be observed in cyp17a1 KO zebrafish with WT females. (S and T) Quantification of frequency and duration of intimate contacts during 5 min (<2 cm). Con, control. T, testosterone. 11-KT, 11-ketotestosterone. *, p < 0.05. **, p < 0.01.