Encyclopedia of Reproduction. Photoperiodism in Fish

Fish reproduction is a rhythmic process occurring at particular times of day and year. Photoperiod is the most predictable and powerful environmental synchronizer of reproduction and entrains biological clocks, which allow anticipating the variations of this environment. Temperature is another rhythmic factor used by fish to adjust their metabolic and physiological processes. The pineal organ plays a key role in transducing photoperiod and temperature cycles and controlling the daily and annual reproductive rhythms. We review here how the pineal photoreceptors integrate photo-thermo-periodic information, and produce rhythmic neural and neuroendocrine messengers, including melatonin, which modulate the daily and seasonal production of brain/pituitary/gonad hormones involved in fish reproduction.