Planlrto~i samples were collected fromKotmale reservoir, at approxi- mately monthly intervals from August 1990 to August 1991. Investigations werc foc~ised on species composition, seasonal variation, vertical and horizontal distrjbution ancl the size class distribution in the population structure of' zooplanlcton. Two species of cyclopoids, two species of calanoids, nine species of claclocerans
... [Show full abstract] ancl sixteen species of rotifers were recorded. Among these, the most abundant species during the study period wereMesocyclops sp,Plzyllodiaptonrus UIL,LCL~, Ccriodc~phl~ia col.nc~ta, Kcratella tl-opica, Filina lo~zgiseta, B~-nchio~z~rs cnrrdntzrs and TJ-icocer-cc' sinrilis. A location at the deepest region of the reservoir closer to the dam was selectei as a representative station to investigate the vertical distribution of zooplanlcton. At this location, the vertical distribution patterns of all the zooplanlcton werc almost similar throughout the year. As this location is situated at the down stream region of the river, it was expected to contain most of the zooplanlrton of the reservoir. The horizontal distribution of zooplankton dicl not show much variation. The nauplii stages and cyclopoids showed highest abundance in the population of zooplanlrton. However,during most of the months, the adult stages of calanoids and cladocerans were highly