Oceanological and Hydrobiological Studies International Journal of Oceanography and Hydrobiology Vol. XXXV, No.1 Institute of Oceanography (29-37) 2006 University of Gdańsk Research Article Diel vertical distribution of zooplankton in Piaseczno Lake (Wdecki Landscape Park) – II. Rotifera GRZEGORZ GRZEGORZ, PIOTR KLIMASZYK, NATALIA KUCZYēSKA- KIPPEN  Department of Water Protection, Adam Mickiewicz University Drzymały 24, 60–613 Poznań  kippen@hot.pl Key words: diel vertical migration, rotifers, vertical distribution, water column Abstract Vertical distribution of chosen species of Rotifera was studied in Piaseczno Lake, during a water stagnation period, in the summer of 2004. Environmental factors, such as temperature, dissolved oxygen and water transparency in the whole water column were measured. The presence of a total of 45 species of Rotifera was found. The analysis of the diel vertical distribution of the examined species of rotifer communities revealed differentiated models. Diel vertical migrations were observed in the case of Gastropus stylifer, Asplanchna priodonta and Trichocerca similis. The remaining species (Kellicottia longispina, Polyarthra dolichopter and P. vulgaris) did not undergo migrations, they remained within a certain water layer throughout the day and night. These differences in the diel behaviour of particular species of rotifers may be mostly dependent on particular ecological requirements and different forms of predation caused by invertebrate and young fish predators.