Continuous Exposure to Light Suppresses the Testicular Activity in Mozambique Tilapia Oreochromis mossambicus (Cichlidae)

Abstract

Although photoperiod plays a critical role in seasonally breeding fish, effect of altered photoperiod on reproduction of continuously breeding fish is not well understood. The objective of this investigation is to determine the effect of continuous light exposure on testicular activity in Oreochromis mossambicus. The fish were exposed to simulated photoperiod and continuous light for 21 days. Although the mean numbers of spermatogonia and primary spermatocytes did not show significant difference, the mean numbers of secondary spermatocytes, early spermatids and late spermatids were significantly lower in fish exposed to continuous light compared to those of initial controls (fish euthanized on the day of commencement of experiment), controls (fish kept in natural photoperiod) and fish exposed to simulated photoperiod. Furthermore, diminished immunoreactivity of androgen receptors was observed in the Sertoli cells concomitant with significantly lower serum levels of testosterone in fish exposed to continuous light compared to other experimental groups. In addition, the mean serum cortisol levels were significantly higher in continuous light fish group compared to other experimental groups. Overall, these results indicate that exposure to continuous light inhibits advanced stages of spermatogenesis, possibly through the suppression of testicular steroidogenesis and that this effect might be mediated through the stress-axis in O. mossambicus.