The present study focused on observation of effect of potassium dichromate as standard toxicant on feeding activity of D. magna. Isolated feeding suppression was measured as fluorescence intensity of ingested microbeads by daphnids and expressed as its feeding rate (EC50FI). We calculated the sub-lethal feeding suppression endpoints for 1, 2, 3, 4 and 5 hours exposure in potassium dichromate and compared these values with EC50 concentration of immobilization test of D. magna. The most close to immobilization (EC50)result was obtained as for 4 as well for 5 hours exposure time; however 4 hs exposure was chosen as more adequate exposure time for our design of feeding suppression bioassay.