Correlation of testicular melatonin and cellular stress in an annual spermatogenic cycle of Clarias batrachus

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 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), percentage of haploid cells by using DNA intercalating dye in the seminiferous tubules, melatonin concentrations and different intracellular stress parameters in the testis. The concentration of melatonin displayed a distinct seasonal pattern, reaching its peak during the “phase of functional maturity”. Interestingly, the levels of 2′,7′–dichlorofluorescein [reactive oxygen species (ROS) marker], malondialdehyde (MDA) and total nitrate [reactive nitrogen species (RNS)] were found significantly lowered at the verge of “mature state”. Correlation and LOESS (Locally Estimated Scatterplot Smoothing) 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 cellular stress to augment the quality of germ cells required for seed production in the culture of any fish species.