THE IMPACT OF MATURE CYPRINID FISH ON THE COMPOSITION AND BIOMASS OF BENTHIC MACROINVERTEBRATES

The effects of predation by mature cyprinid fish on the composition, b iomass and seasonal dynamics of macroinvertebrate biomass were investi gated in fishpond experiments. Different sized adult bream (Abramis br ama L.) and carp (Cyprinus carpio L.) were stocked at different densit ies. Benthivores were forced to feed on benthos by introduction of pla nktivorous perch (Perca fluviatilis L.) fry. Total dry biomass of bent hic macroinvertebrates was not clearly reduced neither by large nor by small bream stockings. Carp significantly reduced the biomass of tota l benthos. Some members of the benthos might be influenced by fish onl y indirectly contributing to formation of new microhabitats preferred by these invertebrates.