Evolutionary insights and expression patterns of sex-related gene families in the zig-zag eel Mastacembelus armatus.

The zig-zag eel exhibits both sexual dimorphism and sex reversal, making it crucial to understand the mechanisms of sex determination and differentiation. Additionally, the wild populations of the zig-zag eel are significantly declining, emphasizing the need for urgent conservation efforts. In this study, we identified 7 Dmrt, 62 HMG-box, and 73 TGF-β family members in the zig-zag eel genome. Evolutionary analysis revealed that the HMG-box and TGF-β families in the zig-zag eel are primarily characterized by purifying selection. Furthermore, we identified 52 differentially expressed genes between males and females, with more male-biased genes than female-biased genes within these three gene families. ZzDmrt2a was highly expressed in the ovary, while ZzDmrt2b was highly expressed in the testis. Interestingly, Zzgdf9, located on the Y chromosome, was significantly expressed in the ovary. Our results highlight the complexity of sex differentiation mechanisms and underscores the importance of further research to elucidate the specific functions and regulatory networks of these sex-biased genes. Such insights could inform breeding strategies in aquaculture, contributing to the conservation and management of the zig-zag eel.