Spermatogenesis and reproductive cycle of male piracanjuba (Brycon orbignyanus) raised for use in repopulation programmes

Although Brycon orbignyanus has traditionally been extensively fished in the Parana and Uruguay basins, anthropic events and fishing pressure have substantially diminished natural stocks. Restocking programmes have, nevertheless, aided efforts to restore the stocks of this fish in its former ranges. The objective of this study was to characterize the spermatogenesis and reproductive cycle of male B. orbignyanus maintained in a commercial fish hatchery for use in future repopulation programmes. For this purpose, we monitored patterns of gonad development and variations in the gonadosomatic index of B. orbignyanus individuals through time. Biometrics and sample collections were performed for macroscopic and histological analysis of two groups of individuals with age ranging from 21 days after fertilization (DAF) to 821 DAF (Group 1) and from 976 DAF to 1416 DAF (Group 2). At each time point, testes of euthanized fish were collected for histological analysis. Testes were found to be composed of anastomosed seminiferous tubules and tubular compartments, being classified as anastomosing tubular. Five reproductive phases of B. orbignyanus were identified and described under captive conditions, namely immature, initial developing, developing, spawning capable and regressing. The "developing" phase was observed at practically all ages and in all four seasons, characterizing a rapid restart of the reproductive cycle of the species, i.e. the short and ephemeral "regenerating" phase. Males of B. orbignyanus maintained in ponds will be able to release sperm between spring and summer, with the regression stage beginning still in the summer.