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Protogynous sex change in sexually immature spotty wrasse (Notolabrus celidotus)

One of the most unique forms of sexual plasticity can be witnessed in sequentially hermaphroditic fish, which begin as one sex and change to another at some stage in their lifecycle. The endemic protogynous spotty wrasse (Notolabrus Celidotus), has historically been considered monandric although two male morphs appear to exist. To date the majority of research has focused on sexually mature females that are changing sex to become terminal phase males. The current study seeks to describe sex change in sexually immature females that are transitioning to become initial phase males. This was achieved through analysis of gonadal histology as well as expression of three key sex differentiation related genes (amh, dmrt1 and cyp19a1a). Fish (n=141) were caught from the Tauranga Harbour ranging in size from 52-270 mm TL from May-June 2022. The smallest transitional fish identified was 52 mm TL and the smallest IP male detected in this study were 72 mm TL, indicating IP male spotty wrasse likely reach sexual maturity at a much earlier and smaller developmental stage than previously realised. Expression of amh and dmrt1 showed a clear male-bias across sex change, with the former being upregulated in early sex change. The aromatase gene, cyp19a1a showed an overall female-biased expression pattern despite having some unexpected upregulation in the mid stages of sex change. The results supported previous reports that all juvenile spotty wrasse are female first before some individuals undergo pre-maturational sex change to become IP males. Having clarified the process of sex change leading to IP male formation and considering data from other studies of IP and TP testicular structure in this species, it seems no longer tenable to consider them monandric.
Type of thesis
The University of Waikato
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