Germ cell proliferation and apoptosis during testicular regression in a seasonal breeding fish kept in captivity

[Display omitted] •Germ cell proliferation and apoptosis were related to fish spermatogenesis in captivity.•Higher PCNA/TUNEL ratio occurred in the breeding season.•Apoptosis is more abundant in the meiosis than mitosis during testicular regression.•Males maintain a considerable stock of spermatozoa in the tubular lumen during resting.•Germ cells pool is regulated by a shift in cell proliferation and apoptosis balance. Cell proliferation and apoptosis regulate germ cells stock and sperm production, eliminate anomalous gametes, and are essential parameters to consider in fish farming. Herein, spermatogenic activity as well as germ cell proliferation and apoptosis were assessed in Leporinus taeniatus, a seasonal breeding species from the São Francisco River basin, Brazil. Testes of 24 adult fishes from a farming station were sampled between December and July and processed for light and transmission electron microscopy and immunohistochemistry for PCNA and TUNEL assay. The gonadosomatic index and seminiferous tubule diameters presented higher values during the breeding season (December/January and February/March), and then significantly reduced during the regression and resting stages (April/May and June/July). Phagocytosis of spermatozoa by Sertoli cells was evident during gonadal regression, but a significant number (up to 30%) remained at the tubular lumen during the resting stage. A higher PCNA/TUNEL ratio occurred in the breeding period, leading to an elevated proportion (%) of spermatogonia (GA and GB) in resting. Moreover, a higher TUNEL/PCNA ratio indicates the contribution of apoptosis to the reduction of germ cells during testicular regression. Together, these results indicate a shift in the balance between cell proliferation and apoptosis that contributes to the regulation of the spermatogenic cycle and germ cells pool of L. taeniatus kept in captivity.