Peripheral administration of Kiss1 pentadecapeptide induces gonadal development in sexually immature adult scombroid fish.

Kisspeptins have emerged as potent regulators of the reproductive brain-pituitary-gonad (BPG) axis. Our previous study demonstrated that the brain of the chub mackerel (Scomber japonicus)， a scombroid fish， expresses two kisspeptin-encoding genes， kiss1 and kiss2， and exhibits sexually dimorphic expression profiles. Recent studies strongly suggest that teleost Kiss1 and Kiss2 precursors produce mature Kiss1-pentadecapeptides (Kiss1-15) and Kiss2-dodecapeptides (Kiss2-12)， respectively. In light of the above， the present study evaluated the potency of synthetic peptides of Kiss1-15， Kiss2-12， and a GnRH analog (GnRHa) on inducing gonadal development in sexually immature adult chub mackerel. Synthetic peptides were administered subcutaneously through mini-osmotic pumps. On day 45 post-administration， gonadosomatic index (GSI) values (%) of male fish treated with Kiss1-15 (1.82) significantly increased in comparison to initial control (0.33)， final control (0.49)， Kiss2-12 (0.24)， and GnRHa (1.13)-treated fish. Interestingly， the testis of all Kiss1-15 treated fish revealed spermiation， and were full of spermatozoa. These fish showed significantly higher levels of pituitary fshβ and Ihβ mRNAs and circulating 11-ketotestosterone. GnRHa treated fish also revealed the presence of few spermatozoa in the testis. In females， no significant changes in GSI values were found between treatments; however， Kiss1-15- and GnRHa-treated fish showed prominent signs of vitellogenic onset， with many early yolk oocytes in their ovaries. Interestingly， Kiss1-15-treated fish exhibited higher levels of pituitary fshβ and circulating estradiol-17β. These results indicate that peripheral administration of Kiss1-15 and GnRHa can induce gonadal development in sexually immature chub mackerel.