The sbGnRH-GTH system in the female short mackerel, Rastrelliger brachysoma (Bleeker, 1851), during breeding season: implications for low gamete production in captive broodstock.

The short mackerel (Rastrelliger brachysoma) is one of the most economically important fish in Thailand; it is also a prime candidate for mariculture but unfortunately is plagued by reproductive problems that cause low production of gametes in captivity. An understanding of how the brain, pituitary, and gonad axis (BPG) from the neuroendocrine system are involved in the reproductive activity of wild and captive R. brachysoma should help clarify the situation. In this study, we investigated changes in the sea bream gonadotropin-releasing hormone (sbGnRH)-gonadotropin (GTH) system in the female short mackerel, Rastrelliger brachysoma (Bleeker, 1851), during breeding season. sbGnRH-immunoreactive (ir) cell bodies were detected in the nucleus preopticus-periventricularis including nucleus periventricularis (NPT), nucleus preopticus (Np), and nucleus lateralis tuberis (NLT). Additionally, the sbGnRH-ir fibers protruded into the proximal par distalis (PPD) where GTH (FSH and LH) cells were detected. The number of sbGnRH-ir cell bodies and GTH cells and level of LH mRNA were significantly higher in the breeding season than those in the non-breeding season. Moreover, the number of sbGnRH-ir cell bodies and GTH cells and levels of sbGnRH and GTH (FSH and LH) mRNA were significantly higher in the wild fish than those in the cultured broodstock. It is suggested that the wild fish tended to have better reproductive system than hatchery fishes. This could be related to the endocrinological dysfunction and the reproductive failure in the hatchery condition. Moreover, the changes of all of the hormonal level could potentially be applied to R. brachysoma aquaculture.