Hunger-induced foraging behavior of two cyprinid fish: Pseudorasbora parva and Rasbora daniconius

Abstract

The feeding and swimming behaviors of Pseudorasbora parva and Rasbora daniconius (Cyprinidae) with two different prey types (Daphnia pulex and Artemia salina) at different densities (0.5, 1, 2, 5, 10, or 25 per l) were studied after 36 h of food deprivation. Full satiation was defined as the cumulative number of attacks performed until fish attain a constant attack rate which for P. parva was 425 and R. daniconius was 390 attacks. Initial feeding rates showed marked variation with prey availability. Feeding rates of fish in high prey concentrations were higher at the beginning of the experiment and decreased faster than in low prey densities. Decreases in the feeding rate at high prey densities were due to faster attainment of satiation. Feeding rates of fish across high prey densities reached a steady level after satiation. Swimming speeds of fish were inversely proportional to prey density. Moreover, the change in swimming speeds was directly related to the level of satiation. The ratios of the attack rate and the encounter rate against prey density of both fish reveal that the search for prey triggered swimming and thereby feeding during the transition from hungry to satiation. The findings of this study demonstrate that satiation plays an important role in fish foraging that should be considered a significant factor in foraging analysis.