Changes in Fish Community of Klíčava Reservoir with Particular Reference to Eurasian Perch (Perca fluviatilis), 1957–72

Soon after the 1955 filling of the 60 ha mesotrophic Klíčava Reservoir in Czechoslovakia, the fish fauna started to change. Generally, lithophils were replaced by phytophils and then by ecologically more plastic species. Fish biomass increased in the first 12 yr from 65 to 236 kg/ha, but after 1967 dropped to about 170 kg/ha. Increased biomass and density of piscivores were responsible for the decline. Among the piscivores the most important role was played by the pikeperch (Stizostedion lucioperca) rather than the Eurasian perch (Perca fluviatilis) or northern pike (Esox lucius). Cyclical changes in the age structure of the perch population and the periodical occurrence of many young resulted from fluctuations in the rate of cannibalism, which affected the density of the fry and yearlings. A decline in zooplankton biomass and disappearance of larger zooplankters in the first 5–6 yr of the reservoir were due to increased density of fish, especially perch, which fed on zooplankton. Synchronous predation by piscivores and zooplanktivores produced a nearly stable zooplankton biomass in the later years of the reservoir. The perch is a highly specialized species which behaves in the fish community more or less autonomously, because it is able to control its own density in accord with its food resources. The above conclusions are based on a literature review and analyses of new data. Key words: Percidae, community ecology, Perca, biomass, density, production, predation