The Neotropical catfish Steindachneridion parahybae (Siluriformes: Pimelodidae) is a freshwater catfish, endemic to the Paraíba do Sul River Basin and seriously endangered in this basin. In the present study we describe an occurrence of an intersex individual in S. parahybae, including histological analysis of the gonads and cytogenetic of this juvenile. Additionally, we compared this animal to others animals from the same breeding batch (males and females). This result may provide support for the knowledge of the reproductive physiology of this threatened species in captivity, which is the basic premise for the program of fish restocking of S. parahybae in Paraíba do Sul River Basin and its tributaries. Link