Differences in distribution of NPY and NPY receptors in a sex changing fish

Saddleback wrasse (Thalassoma duperrey) a protogynous sex-changing fish from the Hawaiian Islands, have behavioral differences based on sex and social roles. Dominant, territorial terminal phase (TP) males can develop from either females or initial phase (IP) males. Previous work indicates that neuropeptide Y (NPY) can stimulate release of gonadotropins in fishes. Additionally, NPY has been show to stimulate sex reversal in the congener T. bifasciatum. NPY and peptide YY (PYY) are closely related peptides that bind to the same receptors. Fish were collected from reefs during time of daily mating. PYY was labeled with [sup.125]I and applied to brain sections to determine receptor distribution. Anti-NPY was also applied to sections to determine peptide distribution. Females had receptor binding in the dosomedial zone. TP males had receptor binding in hypothalamic, preoptic area (POA) and tuberal nucleus. All three phenotypes had receptor binding in optic tectum (OT). Distribution of NPY-like immunoreactivity (NPY-LI) occurred in the same regions as receptor binding. The fact that NPY-LI and receptors are found in OT of all fish is probably related to vision. The differences in phenotypes suggests that in this species NPY affects regulation of sex or sex roles. T. duperrey demonstrates sexual plasticity via protogyny. NPY could play a role in maintaining the sexual status of individuals in this system when social cues inducing sex reversal are absent. The presence of NPY-LI in the POA of TP males corresponds with earlier results in T. bifasciatum indicating that TP males have greater GnRHir in POA. This suggests that NPY plays a role in maintenance of sexual status of TP males, likely via control of GnRH.