Zooplankton Feeding in Common Bream (Abramis Brama), White Bream (Blicca Bjoerkna) and Roach (Rutilus Rutilus): Experiments, Models and Energy Intake

Abstract

Three models of the sieving mechanism of the branchial sieve were used to predict the ability to retain zooplankton of three sympatric cyprinids: common bream, white bream and roach. The model predictions were tested with filter-feeding experiments, using three size classes of each species. Results of experiments in darkness corroborated closely with the reducible-channel model for common bream (retention in the medial channels on the gill arches; the diameter of these channels can be reduced with the lateral rakers), rather well with the unreducible-channel model for white bream (the channel diameter cannot be reduced) and possibly with the saw-tooth model for roach (retention on the gill slits). Common bream can adjust the mesh size of its branchial sieve, thus achieving a higher flexibility in food uptake than the other two species. In light experiments, roach and the small common and white bream switched to particulate intake, characterized by a lower retention ability and a higher filtering rate than during gulping. The retention ability was used to calculate the percentage of the available zooplankton energy that the three cyprinids can retain as a function of the fish's length. This retained energy percentage decreases sigmoidly with increasing fish length. At any length between 10-50 cm, common bream has the highest retained energy percentage, white bream the lowest and roach is intermediate. The population of common bream will therefore be at an advantage in the competition for food when zooplankton is a major food source, like in eutrophic lakes.