Histological and Molecular Characterisation of Gonadal Phenotypes Confirms Diandry in a Protogynous Wrasse

Sequentially hermaphroditic fish begin life as one sex and change to another at some stage of their lifecycle. To date, the majority of research into this fascinating process has focused on sex change in sexually mature fish. The current study on the New Zealand spotty wrasse (Notolabrus celidotus) seeks to describe sex change in sexually immature females that are transitioning to become so called initial-phase males. This was achieved through analysis of gonadal histology, and the expression of key genes involved in sex differentiation (amh, dmrt1, and cyp19a1a) and methylation (dnmt1 and dnmt3a). It was found that initial-phase (IP) male spotty wrasse likely reach sexual maturity at a much earlier developmental stage and smaller size than previously realised. This study furthermore shows that all juvenile spotty wrasse are female first, before some individuals undergo pre-maturational sex change to become IP males. Thus, we confirm diandry in the protogynous New Zealand spotty wrasse and provide clarity around the definitions of primary male formation.