Involvement of galanin in reproduction of male tilapia, Oreochromis mossambicus.

Galanin(GAL) is recognised for its involvement in various physiological, behavioural, and neuroendocrine functions in vertebrates. Yet, the impact of this peptide on spermatogenesis in fish remains understudied. In this investigation, the administration of 5 µg of GAL receptor agonist (GAL-A) to the tilapia Oreochromis mossambicus did not significantly alter the numbers of different germ cells except for a significant rise in the number of late spermatids compared to the control group. By contrast, treatment with 20 µg of GAL-A caused a significant rise in all germ cell counts and tubule and lumen areas and a significant reduction in the area of interstitium relative to the control group. The numbers of spermatogonia-A, primary and secondary spermatocytes, and early spermatids showed a strong positive association with regard to their respective cyst size. Furthermore, fish administered 20 µg of GAL-A exhibited significant increases in the percentage of GnRH-immunoreactive fibres within the nucleus lateralis tuberis and proximal pars distalis of the pituitary gland, concomitant with significantly higher serum levels of LH, and the intensity of androgen receptor protein expression in the testis when compared to control groups. The in vitro experimental results revealed a significantly increased level of 11-KT in the testis treated with 30 or 300 µM of GAL-A when compared to the control group. Together, these results demonstrate for the first time that GAL-A enhances spermatogenesis and steroidogenesis in the testis. GAL-A may influence these effects through the hypothalamic-pituitary axis and directly at the testicular level in teleosts.