Continuous Exposure to Light Suppresses the Testicular Activity in Mozambique Tilapia Oreochromis mossambicus (Cichlidae
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ontinuous Exposure to Light Suppresses the Testicular Activity in Mozambique Tilapia Oreochromis mossambicus (Cichlidae) P. Konkala and C. B. Ganesha, * a
Department of Studies in Zoology, Karnatak University, Karnataka state, Dharwad, 580 003 India *e-mail: [email protected] Received September 16, 2019; revised December 9, 2019; accepted January 10, 2020
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. Keywords: tilapia, Oreochromis mossambicus, continuous light, androgen receptor, spermatogenesis DOI: 10.1134/S0032945220040074
External factors are known to influence various physiological functions in fish (Hilder and Pankhurst, 2003; Chernyaev, 2007). Among several factors, photoperiod acts as an environmental cue and regulates the timing of reproduction in fish (Imsland et al., 1997; Bayarri et al., 2004; Lombardo et al., 2014). Exposure to continuous light (CL) during the final stages of reproduction alters the timing of spawning in the pikeperch Sander lucioperca (Sarameh et al., 2012; Ben Ammar et al., 2015), whereas inhibition of gonadal growth, testosterone secretion and precocious maturation are observed in the European seabass Dicentrarchus labrax (Rodriguez et al., 2005; Bayarri et al., 2009). Similarly, exposure to CL suppresses the testicular development in the juveniles of the Nile tilapia Oreochromis niloticus (Rad et al., 2006; Navarro et al., 2015) and affects spermatogenic cysts recruited into spermatogenesis in the Atlantic cod Gadus morhua (Almeida et al., 2008). Likewise, exposure to CL either retards the gonadal development in the rainbow trout, Oncorhynchus mykiss (Noori et al., 2014) or block
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