Studies on fish feeding rhythms and their application

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1. Fish can learn demand feeding by operant conditioning. We kept red sea bream, goldfish and masu salmon by demand feeding method. Feeding and locomoter activity rhythms were simultaneously recorded. As the results, (1) these species easily learned demand feeding both individually or in groups. We could keep them longer only by this method. (2) Demand feeding showed better growth rate than the regular way of restricted feeding, especially in goldfish. (3) Circadian rhythms of both feeding and locomotor activities were confirmed under constant conditions, suggesting the existence of biological clock in these species.2. Multiple oscillators are assumed to be involved in the fish circadian system of locomotor, feeding and physiological functions. Correlation between oscillators and functions, however, are still controversial. Location of biological clock was investigated from the study of melatonin, the time-keeping hormone. As the results, (1) we found that goldfish eye has the biological clock. (2) There were no positive data on biological clock in the pineal organ of masu salmon and European sea bass, and the eye of European sea bass. (3) Melatonin profile in the eye of European sea bass under light-dark cycle displayd reversal pattern compared to the other fish species. (4) Melatonin receptors in the brain of goldfish coupled with G-proten. Daily rhythms of these receptors were down regulated by the pineal melatonin.