Administration of Exogenous Kisspeptin Induces Breeding Competence in Post-pubertal Female Common Carp (Cyprinus carpio).

Puberty is a crucial stage in vertebrates, controlled by complex neuroendocrine mechanisms, yet its precise pathways remain unclear. Kisspeptin and melatonin are central to this regulation, acting as opposing forces: kisspeptin activates the hypothalamic-pituitary-gonadal (HPG) axis, while melatonin suppresses it. Serotonin also influences GnRH secretion. Despite advancements, identifying novel hormonal agents is crucial for enhancing reproductive outcomes in artificial propagation. Therefore, this study aimed to investigate the effects of kisspeptin administration on the pubertal onset and reproductive efficiency in female Common carp (Cyprinus carpio), alongside its interaction with melatonin and serotonin in modulating the neuroendocrine reproductive axis. Common carp (6 ± 1.5 cm, 5.5 ± 2 g, and 5-6 months old) were divided into control, low-dose kisspeptin (100 ng/g), and high-dose kisspeptin (250 ng/g) groups. Fish received biweekly intramuscular kisspeptin injections for 4 weeks. Post-treatment, the brain and gonads were analyzed for hormonal assays, gene and protein expression analysis, and histology. Kisspeptin significantly increased gonadotropins, sex hormone, and serotonin while reducing melatonin levels. Key HPG axis genes (kiss1, kiss2, kiss1r, gnrh2, gnrh3, gth1r, gth2r, esr1) and serotonin receptor (htr1ab) were upregulated, whereas melatonin receptor (mtnr1a) and gnih were downregulated. Protein expression mirrored these results, showing increased levels of Kiss1, Kiss1R, 5-Ht2A, Gnrh2, and Esr1, with reduced Mtnr1A. Histological analysis revealed enhanced gonadal development, with more advanced oocytes in the higher-dose group. These findings demonstrate that kisspeptin accelerates puberty and enhances reproductive development in Common carp, offering significant potential for optimizing aquaculture breeding practices.