In the years 1996-1999 the authors studied fertility of females of seven zooplankton crustacean species of the genus Eudiaptomus (2 species), Bosmina (4) and Daphnia (1) in six lakes of various trophic states from oligotrophic (Lake Biaµe) to distrophic (Lake Konopniak and Lake Suchar Zachodni) in the Suwaµki District. Water samples were collected every three months at the same sites to analyse 20 physico-chemical parameters. Chlorophyll a and b and carotenoids were evaluated as the food content indices in phytoplankton as a whole and separately in cells smaller than 50 mm.
The study has revealed that the highest female fertility in Copepoda representatives (genus Eudiaptomus) occurs in spring, while in Cladocera individuals (genus Bosmina and Daphnia) - in summer. Generally, both in Copepoda and Cladocera representatives the number of laid eggs increases and their size decreases with the rise in lake trophic state.