Gonadal development period and sexual differentiation through histological analysis in Brycon orbignyanus (Valenciennes, 1850) (Characiformes: Bryconidae)

The aim of this study was to investigate the labile period of gonadal development in Brycon orbignyanus maintained under cultivation conditions and contribute to the creation of protocols for the sexual manipulation of the species. A histological analysis observed that gonadal differentiation (testicular and ovarian) started amid the population 296 days after fertilization and comes to completion in 100% of individuals at 730 days after fertilization, when males with developing gonads were observed, while females remained immature. All individuals larger than 27 cm already had their reproductive organs completely formed. The structuring of supposed ovaries and testicles was similar, from the formation of continuous strings of germ cells to the gradual isolation of these by somatic cells for the formation of cysts of oogonia or spermatogonia. After the formation of cysts, germ cells enter meiosis to form primary growth oocytes and spermatocytes, a moment when secondary structures also emerge with the formation of the ovigerous lamellae, tunica albuginea and germinal epithelium. It is concluded that the labile period of gonadal development in the species occurs at 323 days after fertilization under the conditions of the present experiment.