Growth hormone (GH) has pleiotropic functions in all vertebrates. In addition to its essential role in the regulation of body growth and development, it can also influence reproduction, immunity, osmoregulation, and behavior Immune and neuroendocrine systems have bidirectional communications and it is well document the enhancing action of GH on teleost immune system .It is desirable controlled GH administration to allow growth and stimulation of the innate immune system of fish. In this study, we have characterized a chemical peptide compound, A228, designed by molecular modeling, which is able to perform the function of a GH peptide secretagogue . In pituitary cell culture, the peptide A228 induces GH secretion. It is able to increase superoxide production in tilapia peripheral blood leukocytes cultures and in a macrophage cell line J774 from mice, therefore using this molecule, innate immune system stimulation is obtained in vitro both in fish and in mammals cell cultures. In this paper is also shown the biological action in vivo of the molecule, to assess growth stimulation in tilapia larvae.