Life strategy and feeding relations of populations of the cyclopoid copepods were studied in two deep and stratified reservoirs in Czech Republic. Cyclopoid copepods were represented mostly by Cyclops vicinus and contributed significantly to the spring biomass of zooplankton. Long-term monitoring of seasonal dynamics and instar analysis were used to evaluate life strategy. Short-term feeding experiments in small containers irt situ! and long-term experiments in large plastic enclosures (1.7 m diameter, 8 m depth) constructed in one of the reservoirs were used to study the carnivorous feeding of cyclopoid copepods. Cyclops vicinus exhibited a pronounced seasonal changes of the population density and instar composition, with regular diapause and sharp spring increase of both density and feeding activity. Data are presented an the impact of its predatory feeding on herbivorous zooplankton species. The life strategy of Cyclops vicinus is clearly opportunistic using periods of available food far population increase:dense algal blooms in spring provide food for nauplii to survive and complete larval development and subsequent zooplankton prey to reach maturity and to produce eggs.