Ontogeny and distribution of gonadotropin-releasing hormone (GnRH) neuronal systems in the brain of the cichlid fish Cichlasoma dimerus.

Using immunocytochemistry we have described the distribution and ontogeny of three distinct gonadotropin-releasing hormone (GnRH) neural systems, emphasizing the analysis during the period of sex differentiation in the South American cichlid fish Cichlasoma dimerus. In the forebrain a group of neurones immunoreactive to salmon GnRH that formed clusters in the nucleus olfacto retinalis (NOR), was located at the junction of the olfactory bulb and the telencephalon. These neurones differentiated 3 days after fertilization from the olfactory placodes.