Histological notes on diandric protogyny in the freckled hawkfish Paracirrhites forsteri (Cirrhitidae) from Kuchierabu-jima Island, Japan

This study used histological techniques to investigate sexual patterns in the freckled hawkfish Paracirrhites forsteri, which has a mating system intermediate between harem and male-territory-visiting polygamy. Males on reefs in the area of Kuchierabu-jima Island tended to be larger than females, and one hermaphrodite with ovarian cavities was observed at a size intermediate between most males and females. These findings indicate a protogynous sexual pattern in the studied population. However, some males were smaller than females, with the smallest individual collected being a male. Furthermore, most individuals with a body size smaller than that typical of females exhibited bisexual gonads. These new findings suggest that prematurational sex change occurs in this species, whereby some males derive directly through sexual differentiation as juveniles. Our study represents the first report suggesting diandry in the Cirrhitidae.