RESUMEN
In the present study, water samples from 3 stations of Kor river, Iran were analyzed for seasonal fluctuation of physico-chemical parameters, i.e. air and water temperature, dissolved oxygen, BOD, COD, total nitrogen, total hardness, pH, alkalinity, acidity, total dissolved solid and water current. Effect of physico-chemical parameters on surface water density of rotifers was also studied. During one year study 13 species of rotifers belonging to 2 classes and 3 orders, 6 families and 10 genera were recognized. Maximum population density belongs to Lecane luna and the minimum population density was observed in Keratella valga and Monostyla lunaris. An inverse relationship between the population density of rotifera and the water current as wall as a direct relationship between the water temperature and the population density of rotifers was observed in all sampling stations and throughout the study period.