Objective  Expression and location of cyp19a1a important in the gonadal development and sex determination of bony fishes were studied to pave the way for breeding all-male Silurus lanzhouensis.

  Method  The gene in the sexual organs of S. lanzhouensis were cloned, and expression of hermaphroditic parents of YY super-male individuals verified. The full-length cDNA sequence of cyp19a1a was obtained by homologous cloning and rapid amplification of cDNA ends (RACE). Expressions of the gene in 3-month-old, 1-year-old, and 3-year-old normal female and male as well as 3-year-old hermaphroditic fish were determined by real-time fluorescence quantitative PCR (qRT-PCR). Expression and localization of the gene in tissues of 3-month-old, 1-year-old, and 3-year-old normal female fish were determined using immunohistochemistry (IHC).

  Result   The full length of cyp19a1a cDNA was 2168 bp, which included 5' untranslated region (UTR) of 53 bp, open reading frame (OFR) of 1707 bp, and 3' UTR of 408 bp, encoding 568 amino acid residues with a conserved functional region of aromatase. Cyp19a1a mRNA was mainly expressed in the gonads. The expressions in 3-year-old hermaphroditic and normal individuals were not significantly different (P＞0.05), but significantly higher in ovary than in testis, and significantly intensified along with the development of gonad in the bred normal fish. The IHC showed the oogonia distributed only in the ovaries of 3-month and 1-year-old fish at different stages with no positive signals. Whereas the oocytes were found during all development periods with a gradually increasing signal. They existed mainly in the cytoplasm from 3-month to 1-year-old, but in the 3-year-old fish in the follicular membrane, radiation membrane, and sheath cells, in addition to cytoplasm. On the other hand, cyp19a1a was only weakly expressed in the interstitial cells of the testis at different developmental stages of a fish.

  Conclusion   There was a significant role cyp19a1a played in the ovarian development, oocyte growth, and oogenesis. It involved in the testicular development and maintenance and spermatogenesis of normal or hermaphroditic S. lanzhouensis identically.