Gonadal structure and expression localization of sex-related genes in the hermaphroditic grouper Epinephelus akaara (Perciformes: Epinephelidae)

Abstract

As a hermaphroditic fish with considerable economic value, the Hong Kong grouper (Epinephelus akaara) has suffered a continuous decline in wild resources from long-term overfishing and habitat destruction, while with artificial propagation, the low proportion of male fish has always been a difficult problem to address. Understanding the gonadal structure and sex differentiation mechanism of this fish is the key to proposing effective solutions. For many hermaphroditic species, the gonad is observed to be separated into testicular and ovarian parts by a physical boundary. Notably, in this study, no such structure was found in Hong Kong grouper, implying the uniqueness of its gonadal structure, which may be associated with plastic sex. The analysis of important sex-related genes in Hong Kong grouper showed that the expression pattern of vasa, dmrt1, and foxl2 was similar to that of most gonochoristic and other hermaphroditic fishes, indicating the conserved functions of those genes. Unlike previous descriptions in other fish species, the unique expression pattern of foxl3 in Hong Kong grouper revealed its potential function in both female- and male-phase gonads, and we suspected that it might play a crucial role in testicular tissue development and maintenance of functions. This study enables us to obtain a better understanding of sex differentiation in Hong Kong grouper and provides theoretical guidance for artificial breeding in aquaculture.