) females grow two to three times faster than males. Thus, the development of an all-female stock would be of significant benefit for aquaculturestock, investigation of sex determination mechanisms is necessary. The Wilms’ tumor suppressor gene () encodes a zinc-finger transcription factor that plays an essential role in organ development, most notably in the kidney and gonad. Despite its importance for sex determination, information on C. semilaevis WT1a gene was obtained by RACE-cloning. Sequence analysis revealed that the full-length cDNA was 1 886 bp containing a 1 470 bp open reading frame (ORF), a 245 bp 5′UTR. This sequence encoded 489 amino acids containing a KTS alternative splice. Two SSR sequences and two transmembrane helix regions were found in the end of the OFR. We infer that they are gene was highly homologous to that of . An NJ-phylogenetic tree indicated that the fish WT1b gene. Real-time quantitative PCR results revealed that was expressed in the six tissues types examined but was far higher in the gonad. Notably, expression in the testis was significantly higher than that in the ovaries and gonads of sex-reversal female fish. It was lowest in the gonad of sex-reversal female fish. Therefore, we can conclude that is a sex-related gene. The gene was expressed in all of the developmental stages analyzed, from early embryo to 66-day-old fry. Its expression level was highest at neurula stage (20 h) and gently in 16–66 days, however, no abnormalities were observed in the key gonad differentiation stages. Therefore, may be not the key gene controlling gonad differentiation. Our results provide a foundation for the development of an all-female stock and future investigations on the sex determination mechanism. Furthermore, we have provided a good method for identifying the key gene controling gonad differentiation.