INTRODUCTIOn Feeding behavior in Daphnia spp. has long been studied, from the individual to community level, because of its eco- logical importance. Food(or energy) intake is important at the individual and population level because acquisition and allo cation of energy determines developmental rate, growth rate fecundity, and survival, all of which are important components of fitness and determinants of population structure and dy namics[1]. Daphnia spp. are an important component of the zooplankton grazers in lakes because they have high algal grazing rates(because of a relatively large body size) and control phytoplankton biomass and species composition[2,3] Thus, Daphnia spp. provide an important link between dif ferent trophic levels in lake communities and are important prey items for predatory zooplankton[4] and fish[5]. A change in Daphnia spp. population dynamics due to a reduction in deeding rate would be ecologically important because it has the potential to change community structure and function. Sev- eral studies have demonstrated that toxic impairment of feed ing rates at the individual level has direct effects on population parameters such as growth and reproduction 16-8] and indirect effects on community structure, leading to great increases in phytoplankton biomass 19,10] Impairment of feeding rate seems to be a general response toxicant exposure. By exposing Daphnia magna to a range of metals and organic chemicals. Allen et al. 11)demonstrated significant reduction in feeding rates after exposure to all substances tested. Short-term feeding tests have been devel oped with Ceriodaphnia dubia, and under laboratory condi tions have demonstrated contaminant-induced feeding depres- ion after exposure to a range of effluents and toxic substances ith different modes of action[12-14]. Reductions in feeding