RESUMO
Immunoreactive gonadotrophic hormone-releasing hormone (ir-GnRH) was detected in extracts from optic tectum, cerebellum and brain stem of the Venezuelan freshwater fish "caribe colorado", Pygocentrus notatus by means of radioimmunoassay. Like most fishes from the area P. notatus, has a reproductive cycle closely related to environmental conditions changes. Our results show a correlation between gonadal maturation, express as Gonosomatic Index (GI) and the beginning of the rainy season (April-May) in males and females of this species. Fluctuations in the ir-GnRH levels that depend of the reproductive state and environmental conditions occurred in the optic tectum and cerebellum extract obtained from female fish. On the other hand, in males no striking variation were found in any of the structures mentioned, except for the optic tectum, were a significant increase in the ir-GnRH content was observed in May.