Study on the effects of aquatic vegetation on foraging behaviour of planktivores in lakes

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In littoral zones of lakes, macrophytes have considerable structural variation and that provides protection to prey communities by hindering predator foraging. The swimming and feeding behaviour of a planktivore (Pseudorasbora parva) with their prey (Daphnia pulex) were studied in a series of laboratory experiments with varying densities of simulated submerged vegetation. Prey availability was varied from 0.5, 1, 2, 5, 10 and 25 prey.lィイD1-1ィエD1. As the stem density gradually increased, the predator's foraging efficiency decreased considerably relative to feeding in open water. Moreover, a good relation in feeding rate and swimming speed existed with the average stem distance to fish body length ratio. Abrupt reduction in feeding and swimming was recorded when fish body length ratio was near 0.7, which is approximately equal to one stride length of a fish.In fish, hunger increases the motivation to feed and also efficiency of feeding. After 36 hours of food deprivation, the feeding and swimming behaviour of Pseudorasbora parva was studied under different prey densities. The initial feeding rates showed marked variations in relation to prey availability. Under high densities the initial feeding rate of fish was higher and subsequently decreased faster, when compared to those feeding under low prey densities. At high prey densities, two factors are involved : that of high prey encounter rates and also the attainment of food satiation at a faster rate. Across all prey densities, the feeding rates of fish reached a plateau after satiation. The swimming speed was noted as being directly related to the level of satiation. After satiation, the fish fed at a steady rate irrespective of prey density. However, the swimming speed of fish varied significantly in relation to prey density. It was found that the maximum feeding rates depend upon and show a marked variation with average prey distance.