Reproductive indicators during the male sexual maturation of Steindachneridion melanodermatum (Teleostei: Siluriformes: Pimelodidae) in captivity

Abstract

The reproductive dynamics of a species is important information to have for the maintenance and reproduction of animals in captivity, for either commercial or conservation purposes. Steindachneridion melanodermatum is an endemic fish that has been reproduced by breeding protocols, but knowledge related to the maturation and reproductive cycle of this species is scarce. The purpose of this research was to observe different parameters related to the reproductive biology of males born in captivity over a 24-month period to determine the first maturation and reproductive activity of S. melanodermatum males maintained in captivity. Body development changes (weight and length) were observed, and gonadosomatic index (GSI) and plasma sex steroids (testosterone and 17β-estradiol) were measured monthly. Phases of the reproductive cycle were detected based on macroscopic changes and histological observations of the testes. The obtained data were correlated, demonstrating that the GSI values accompanied testis development and sex steroid peaks. Additionally, immunohistochemistry was performed for the detection of KI-67, 3β-HSD and Vasa protein. Our data analysis indicated that the first maturity in males bred in captivity occurred after one year (at 22-month-old fish), with a reproductive period occurring from September to November, which is the spring season in the southern hemisphere.