22 - Melatonin as a potential remedy in fish reproduction against environmental pollution: An emerging issue

Abstract

Melatonin, a pineal hormone, is considered as a light sensitive molecule and is responsible for the regulation of various functions including reproduction. The rhythmic synthesis of this hormone from the pineal organ is synchronized with the environmental light-dark cycle. Alteration of duration and intensity of light exposure affects the rhythmicity of melatonin secretion which utmost alters the functional activity of reproduction. In seasonally reproducing animals, like fish, a cross-talk between the environment and melatonin plays a central role in the maintenance and proper functioning of the gonads to ensure maximum reproductive fitness of the species. With the advancement of technology and urbanization, artificial light at night (ALAN) and organic compounds cause a major threat to the aquatic animals, especially fish, as pollutants. At present, the most pressing and emerging field of endocrine research is the study of impairment of fish production rate because imbalance of sex hormones and redox homeostasis by environmental pollutants, a major concern for socioeconomic status of the farmers. In aquatic system, in addition with ALAN, bisphenol-A (BPA), also negatively modulates the gonadal functions. BPA is mostly present in items made of polycarbonate plastics, epoxy resins, etc. However, it causes increase in the oxidative stress of the gonads which is a very critical factor for the production of good quality seeds in fishery. Unfortunately, till date, the efficacy of melatonin in the restoration of natural fish reproductive physiology against environmental pollution like ALAN and BPA, is totally ignored. A very few mammalian studies showed that melatonin as an antioxidant decreases BPA-induced stress during fertilization by stimulating the antioxidative enzymes. Collectively, from information gathered from different studies it is understood that it will not be unwise to conclude that melatonin may be used as a therapeutic agent in fish reproduction against environmental pollution.