Studies of external ＆ internal factors affecting to the fish demand-feeding.

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To demonstrate the factors affecting to fish appetite, studies of external (light) and internal factor (biological clock) were performed using demand-feeding rhythms of rainbow trout in the initial year, 1999. Based on the results obtained in the previous year, another external factor, food availability, was added. Then, factors affecting to the fish feeding rhythms were analyzed.1. In the first experiment, 24 rainbow trout were used (B.W.105.52±4.04 g). Fish were kept in tanks (46L) individually in which each demand-feeder being set. Experimental regimes were as follows : (1) light-dark cycle (12hr light : 12hr dark) + constant meal (MM), and (2) food cycle (12hr meal : 12 fast) + constant light (LL). Demand-feeding was recorded and compared under these conditions of (1) followed by (2). The results showed that rainbow trout synchronized to LD and food cycle. They displayed higher activity at either light phase or mealtime. However, activity patterns of demand-feeding were different, showing distinct synchronization to light-dark cycle rather than meal-fast cycle. This result suggests that food is also an important external factor as the same as light-dark cycle despite showing different way of synchronization.2. Involvement of biological clock for the expression of demand-feeding rhythms, free-running rhythms was studied under LL and MM conditions. The results demonstrated higher appearance rate of free-running rhythms in the rainbow trout (95%). The results suggest the existence of biological clock synchronizing to food cycle.3. These results demonstrate that daily cycles of both external factors (light and food availability) and circadian internal factor (biological clock) are affecting to the expression of demand-feeding rhythms in the rainbow trout.