Oral administration of the growth hormone secretagogue-6 (GHRP-6) enhances growth and non-specific immune responses in tilapia ( Oreochromis sp.)

Aquaculture is part of the solution for meeting the growing world demand for food, mainly as an animal protein source. However, current yields are insufficient for aquaculture to play this crucial role. Growth-rate enhancement is one of the approaches that have been exploited in this regard. Also, losses caused by bacteria, viruses and parasites remain a significant problem. It has been demonstrated that growth stimulants contribute not only to growth enhancement but also to fish health improvement. Growth Hormone Releasing Peptide-6 (GHRP-6) is one of the earliest-developed, synthetic, peptidyl growth hormone secretagogue receptor agonists. These compounds mimic the effect of the endogenous ligand, ghrelin. This peptide has shown its benefits for both growth enhancement and immune system stimulation in fish. In the present study, we demonstrate that intraperitoneal administration of GHRP-6 induces liver insulin growth factor-I messenger RNA, and increases growth hormone levels in juvenile tilapia (Oreochromis sp.), in a time-course experiment. GHRP-6 also stimulates growth using non-encapsulated and encapsulated peptide administered by a plastic tube to the pharyngeal cavity to juveniles. In addition, administration of GHRP-6 in formulated feed to tilapia larvae was assessed. Growth and immune parameters such as lectin titers and intestinal intraepithelial lymphocyte numbers were increased in treated larvae. Based on these results, GHRP-6 could be an interesting candidate for development into a new biotechnology product for improving fish farming.