Photoperiod, Pineal Photoreceptors and Melatonin as the Signal of Photoperiod in the Regulation of Reproduction in Fish

Annual variation in photoperiod is the most regular phenomenon that has strong predictive value in the temporal organization of seasonal activities in biological world, especially reproduction. Carefully controlled studies demonstrated importance of photoperiods in the regulation of annual reproductive events in diverse groups of animals including fish. Apart from academic interests, study in fish has gained momentum because of its tremendous economic importance as food. Thus, for obvious reasons, efforts are continued to develop technologies for increasing fecundity and growth of fish in culture. As a result, photoperiodic manipulation has emerged as an effective tool of reproductive management in culture fisheries, and understanding the physiology of photoperiodic regulation of fish reproduction became the priority topic of research in different countries. The present paper reviews and summarizes the information gathered in recent years on the importance of photoperiod and the mechanism of photoperiodic signal transduction in the photo-neuroendocrine system in fish emphasizing the role of pineal organ, which is considered as an intermediary between the environment and the endocrine system in vertebrates.