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The effects of submerged macrophytes and light on the foraging behaviour and capture rate of three fishes, perch (Perca fluviatilis), bream (Abramis brama) and roach (Rutilus rutilus), were studied in the laboratory. Attack frequency and number of captured chironomid larvae decreased for all species with increasing complexity of the artifical vegetation. Perch was, however, less affected by vegetation density than bream and roach. Opposite effects were obtained through a reduction of light intensity. Capture efficiency of perch was reduced markedly in darkness, whereas capture efficiencies of bream and roach were unaffected by the absence of light. In a turbid, highly productive lake, the abundance of chironomid larvae increased with increasing submerged macrophyte complexity. Perch was most abundant in Chara tomentosa, whereas bream and roach preferred the unvegetated part of the lake. Perch seem to be the superior foragers on macroinvertebrates in dense littoral vegetation, whereas bream and roach are superior in turbid waters lacking submerged macrophytes. Hence, changes in the physical environment induced by eutrophication (decrease in submerged vegetation and increase in turbidity) should affect the competitive interactions among perch, bream and roach, promoting the observed succession from percids to cyprinids in lakes undergoing eutrophication.
Oikos © 1988 Nordic Society Oikos