The effect of prey size and color of Chaoborus on the predatory response of Lepomis gibbosus.

Abstract

Predation plays a significant role in the structure of the freshwater community. the optimal level of predation by fish depends on the availability and accessibility of prey items in the community. To achieve this optimal level, fish rely mainly on visual stimuli for detection of prey. In our study, we manipulated size and color of prey items to determine the predatory effects of fish. In order to study these effects, we fed Lepomis gibbosus (pumpkinseed) two types of zooplankton. The zooplankton differed in size; Chaoborus flavicans obtained from Lancaster Lake, Cheboygan County, Michigan, were larger than Chaoborus puntipennis, obtained from Douglas Lake, Cheboygan County, Michigan. To determine the predatory effects due to coloration, we dyed the transparent Chaoborus with Rotamin B dye. We conducted six sets of selectivity trials in which the fish were given a choice of Chaoborus for all pairwise combinations. We also observed the feeding response time for the four individual prey items: Lancaster colored, Lancaster uncolored, Douglas colored, and Douglas uncolored. The results of the choice experiments were analyzed using a x2 goodness fit test. The mean response times were compared using t-tests. As expected, our results indicated that both larger size and coloration of prey increased the predatory reponse of pumpkinseed. Studying the predation of fish has an ecological significance because many other populations of organisms are directly or indirectly affected by predatory-prey interactions. Individual and paired feedings were conducted in ten-gallon aquaria. The individual feedings were executed in order to measure average response times, and the paired feedings were done to examine selectivity. The results of both data suggest that size is the more important factor in prey selection. Color contributes to this selection, but does not overcome the effect of size. I concluded that large size is a more important factor than color in fish predation.