• bream;
  • branchial sieve;
  • consumption of meiobenthos;
  • carp;
  • gudgeon;
  • roach

Young individuals of the bottom-biting (i.e. sediment-ingesting) common carp Cyprinus carpio and gudgeon Gobio gobio consumed significant amounts of nematodes in laboratory experiments, whereas the selective-feeding roach Rutilus rutilus did not. In mesocosm enclosure experiments in the field, C. carpio strongly decreased the nematode abundance within 4 days, whereas the bottom-biting bream Abramis brama did not affect the abundance until after 14 days. In controlled experiments with a known number of prey, C. carpio but not A. brama significantly reduced the number of nematodes, and G. gobio reduced the nematode abundance dependent on the size of the fish, with smaller fish causing a greater reduction. Cyprinus carpio consumed the nematodes and did not just mechanically kill them in the sediment, as shown by dissection of the fish intestine. Morphometric analysis of the branchial baskets indicated that the mesh width of C. carpio, but not of A. brama, is suitable for consuming meiobenthos. The results indicate that the meiobenthos is a food resource for certain bottom-feeding freshwater fishes.