Immunolocalization of Serotonergic Neurons during Natural Sex Change in the Hermaphroditic Goby Lythrypnus Dalli

The neurotransmitter serotonin (5-HT) has been suggested to be involved in the inhibition of socially regulated sex change in fish because of its role in the modulation of both reproductive and aggressive behavior. This is the first study looking at the distribution of serotonergic neurons by immunohistochemical techniques at different times during sex change. We set up stable social groups with a male and three females, and sampled the brain of sex changers 2 hr, 1 day, 3 day, 7 days and 14 days after male removal. We also compared males and females with different social status. Immunoreactive neurons were found in the nucleus posterioris periventricularis (NPPv), the nucleus recessus lateralis (NRL), the nucleus recessus posterioris (NRP) and in the raphe nucleus. We measured the total area of NPPv, NRL, NRP, and the number of serotonergic neurons and mean cell area in the raphe nucleus. There was no significant difference in any of the brain regions between males, females or sex changing fish, but there was a slight increase in the number of raphe neurons in the brain of sex changers 2 hr after male removal. The results show that in L. dalli the serotonergic system does not present any morphological sex and status differences, or any dramatic modifications during sex change. These data, together with previous results, do not support the hypothesis of a serotonergic inhibition on sex change.