Understanding neuroendocrine regulatory pathways of sexual behavior in teleosts

The main neuroendocrine pathways of induction of reproductive behavior in fish are elucidated.17α,20β-dihydroxy-4-pregnen-3-one (17,20β-DHP),an oocyte maturation-inducing hormone,was found to act as a pheromone to induce male reproductive behavior.17α,20β-DHP-sulfate (17,20β-DHP-S),a derivative of 17,20β-DHP,was also identified as a later-acting pheromone.In addition,prostaglandin F2 alpha (PGF2α),which is synthesized during female ovulation,has been shown to also act as a pheromone,inducing the final oviposition-inducing behavior to make fertilization successful.It appears that these molecular events are initiated by stimuli from the brain.Numerous neuropeptides have been discovered that promote the initiation of reproductive behavior.Recently,with the proliferation of genome editing technology,a detailed analysis of the molecules involved in these pathways is underway.Analysis of gene knockout in zebrafish and medaka is actively underway.On the other hand,many research reports have shown that the induction pathways of male reproductive behavior are adversely affected by chemical substances.Knowledge of the adverse effects of chemical substances is not only useful as information to prevent their mixing from the viewpoint of protecting the natural environment and as a point of caution in fish farming,but also provides clues for elucidating the pathways of reproductive behavior induction.The elucidation of the pathways of reproductive behavior induction is also important from the point of view of breeding technology for fish farming and biodiversity conservation.In this review,we summarize recent research on the pathways of male reproductive behavior induction in fish and the possibility of developing new aquaculture techniques depending on the results.