10.22376/ijpbs.2019.10.1.p1-12 Volume 11 Issue 4 2020 (October-December) Intense industrialization in India led to release of toxic effluents in surface water bodies causing deleterious effects on freshwater flora and fauna. lessThan i greaterThan Simocephalus vetulus lessThan /i greaterThan (crustacean - cladocera) a tailless fresh water flea is an important member of the zooplankton community and base of the aquatic food chain of freshwater aquatic ecosystems. Fresh water tailless flea, lessThan i greaterThan S. vetulus lessThan /i greaterThan exposed to 5%, 10%, 15% and 20% of SIDCUL Integrated Industrial Estate (SIDCUL-IIE) effluent of Haridwar showed marked changes in behaviour like phototaxis, geotaxis, avoidance activity, appendage movements, swimming, feeding as well as in the morphology, specially in cuticular coloration. The exposed fleas showed hyper activity at initial stage followed by erratic swimming, loss of balance, darkening of carapace, loss of aggressive behaviour and mucous secretion. The food detection and consumption of the fleas was found normal in the initial stage which considerably declined after 48, 72 and 96 hrs exposure of SIDCUL IIE effluent. The phototaxis geotaxis and avoidance indices were found decreased after exposure to 5%, 10%, 15% and 20% SIDCUL IIE effluent, as observed after 7, 14 and 21 days exposure. In the present study it was clearly evident that the intensity of effects was dose and duration dependent. The findings of present study are beneficial for prediction of safe concentration of industrial effluents to be released for well being of freshwater aquatic bodies. The behavioural parameters of the tailless fresh water flea may serve as better biomarkers in relation to industrial effluent toxicity. The role of lessThan i greaterThan S. vetulus is significant lessThan /i greaterThan in environmental monitoring has been discussed. Anand Mishra*, Harnam Singh Lodhi, Sandeep Shukla, Sanjive Shukla and A. K. Chopra Behaviour, Industrial effluent, Simocephalus vetulus. Tailless water flea 46-54