Reproductive biology of an odacine labrid, Odax pullus

The sexual ontogeny of butterfish Odax pullus was examined in the Hauraki Gulf of New Zealand through histological analysis of gonad material, size and age information and seasonal patterns of sexual maturation. The patterns of gonad development and schedules of male recruitment were established and sexual ontogeny of O. pullus was diagnosed as monandric protogyny, with all males developing from mature females after female-to-male sex reversal. All individuals underwent an immature female phase before maturing as functional females at 228·7-264·8 mm fork length (L(F) ) and at 1·1-1·5 years of age, and there was no evidence of a juvenile bisexual phase. Degenerating mature oogenic elements were found in the gonad lumen of individuals with developing spermatogenic tissue, providing histological evidence for functional protogyny. Sex change was estimated to occur at 359-379 mm L(F) and 2-3 years of age. The diagnosis of monandric protogyny for O. pullus coincided with the pattern of sexual ontogeny seen in the majority of labrids, particularly those of the same clade (tribe Hypsigenyini) and contrasted with that seen in a number of other temperate labrids. This study suggests that the protogynous mode of sexual development in O. pullus is likely to be lineage-specific, i.e. associated with the phylogeny of labrid sexual development, and is not constrained by environmental effects on the evolution of sex change in temperate regions.