Abstract
Melatonin, primarily produced by pineal gland, shows a rhythmic pattern of synthesis in response to environmental cues. Hitherto, the role of testicular melatonin in the regulation of annual spermatogenic cycle is indeterminate in any fish species. Present study aims to explore a correlation, for the first time, of melatonin with cellular stress levels in accordance to the rhythmic progression of spermatogenesis through six distinct reproductive phases of an annual gonadal cycle of catfish, Clarias batrachus under natural photo-thermal conditions. We assessed gonadosomatic index (GSI), testicular melatonin concentrations, relative percentage of haploid cells by using DNA dye in the seminiferous tubules, and different intracellular stress markers. The concentration of testicular melatonin displayed a distinct seasonal pattern, reaching their peak during the “phase of functional maturity”. Interestingly, the levels of 2’,7’–dichlorofluorescein [reactive oxygen species (ROS) marker], malondialdehyde (MDA) and RNS (total nitrate) were found significantly lowered at the verge of “mature state”. Correlation and LOESS regression analyses showed a striking positive relationship between testicular melatonin concentration and the activity of antioxidative enzymes, including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione S-transferase (GST). Principal component (PC) analysis also identified the key components of “mature state” viz., GSI, testicular melatonin, haploid cell population (spermatid and spermatozoa), and the activity of enzymatic antioxidants. Cumulatively, melatonin may have a role in growth and maturation of spermatogenic cells by reducing the cellular stress to augment the quality of germ cells required for seed production in the culture of any fish species.