Exposure to Long or Short Photoperiod Affects the Pituitary–Testicular Axis in the Mozambique Tilapia Oreochromis mossambicus (Cichlidae)

In this investigation, we examined the influence of altered photoperiodic conditions on the pituitary-testicular axis in the cichlid fish Oreochromis mossambicus. No significant difference was observed in the mean numbers of spermatogonia and primary spermatocytes across the controls (11.47L:12.13D) or simulated controls (11.45L:12.15D) and fish exposed to short photoperiod (6L:18D). In comparison to controls or stimulated controls, fish exposed to short photoperiod exhibited a significant decrease in secondary spermatocytes, early spermatids, and late spermatids. Conversely, fish exposed to long photoperiod (18L:6D) showed a significantly lower number of all spermatogenic cell types compared to the other experimental groups. These findings were accompanied by a significant decrease in the percentage of luteinizing hormone immunoreactive content in the pars distalis of the pituitary gland, as well as in androgen receptor immunoreactivity, Sertoli cell count in the testis, and serum testosterone levels in fish subjected to short or long photoperiod, when compared to controls or simulated controls. In conclusion, the results of this study indicate that alterations in photoperiodic duration may impede spermatogenesis by suppressing luteinizing hormone secretory activity in the pituitary gland and testicular steroidogenesis in tilapia.