Effects of satiation on feeding and swimming behaviour of planktivores

Hunger affects the feeding and swimming behaviour in fish. After 36 h of fo od deprivation, the feeding and swimming behaviour of Pseudorasbora parva ( Cyprinidae) was studied under different prey densities (0.5, 1, 2, 5, 10 an d 25 of Daphnia pulex per liter). The initial feeding rates showed marked v ariations in relation to prey availability. Under high prey densities, the initial feeding rate of fish was higher and subsequently decreased faster, when compared to those feeding under low prey densities. At higher prey den sities, two factors were involved: that of higher prey encounter rates and also the attainment of food satiation at a faster rate. Across all prey den sities, the feeding rates of fish reached a plateau after satiation. The sw imming speed of fish was found to be negatively related to the prey density and a significant change in swimming speed was noted as being directly rel ated to the level of satiation. It was found that the increasing satiation level greatly influenced the handling time and reactive volume of predator, which finally caused reduced feeding rates.