Clarius fuscus using RT-PCR and RACE. The cDNA was 2 347 bp with a 219 bp 5′UTR, a 596 bp 3′UTR (excluding poly (A)), and a 1 503 bp ORF, which encoded 500 amino acids and had a predicted mol wt of 56.388 kD. Sequence and phylogenetic analyses indicated that the Pelteobagrus fulvidraco, Carassius auratus, . In contrast, there was low sequence identity (<62%) with Cyp19a1b subfamily.This is consistent with the classification based on traditional morphology and biochemistry. mRNA was expressed primarily in the forebrain, hypothalamus, and pituitary, and to a lesser extent in the liver, testis and ovary. We observed differences in the level of expression in brain between males and females ( was expressed prior to sex differentiation in , but there was no difference in the level of expression between prior and post to sex differentiation (12cyp19a1b is not directly involved in mediating sex differentiation in , but may play an indirect role by acting on the hypothalamic-pituitary-gonadal axis.