Seasonal variation, density and diversity of planktonic rotifers in the river Ravi[Pakistan]

A meticulous study was carried out to find out the population density, diversityand seasonal variation of rotifers in the River Ravi for six months from January2002 - June 2002. The plankton samples were obtained monthly using Wisconsinplankton net and the collected samples were stratified by filters of different meshsize and preserved in 4% formalin. A total of 12 species of rotifers were identifiedwhich were Brachionus quadridentata, Brachionus calyciflorus, Brachionus plicatilis,Brachionus caudatus, Keratella valga, Philodina roseola, Polyarthra vulgaris, Platyiaspolyacanthus, Platyias quadricornis, Asplanchna priodonta, Filinia longiseta andCephalodella sp. Water samples were also collected monthly to study thephysicochemical parameters. There was positive correlation between rotiferpopulation and temperature, water flow, D.O., total hardness, chlorides, magnesiumand calcium, but negative correlation between rotifers and pH, total dissolved solids,total alkalinity, CO2 and electrical conductivity.