EFFICIENCY OF FEEDING ON ZEBRA MUSSEL (DREISSENA-POLYMORPHA) BY COMMON BREAM (ABRAMIS-BRAMA), WHITE BREAM (BLICCA-BJOERKNA), AND ROACH (RUTILUS-RUTILUS) - THE EFFECTS OF MORPHOLOGY AND BEHAVIOR

We compared efficiencies of feeding on zebra mussel (Dreissena polymor pha) by three syntopic cyprinids: common bream (Abramis brama), white bream (Blicca bjoerkna), and roach (Rutilus rutilus). Empirical feedin g efficiency (the ratio of food energy content to food capture and pro cessing costs) is largely determined by the time needed to handle prey , rather than by the energy required for specific feeding actions, suc h as detaching and crushing the mussel. The highest individual feeding efficiency values were achieved by large white bream and roach, while common bream performed poorly. Maximal and optimal prey sizes were hi ghest in roach. X-ray movies showed that in roach the dimensions of th e oral gape, pharyngeal slit, and chewing cavity all matched, and thus limited, maximal prey size. In common bream and white bream prey size is limited by pharyngeal crushing power. The ability of roach to proc ess larger mussels is based on the larger static crushing forces that can be exerted by its stout pharyngeal jaws; this could contribute to a strong position in competing for mollusks, most probably at the expe nse of its filter-feeding capacity. An integration of morphology, beha vior, and performance helps to explain feeding efficiency differences among fish species and could eventually provide insights into mechanis ms of trophic segregation.