GILL RAKER STRUCTURE AND SELECTIVE PREDATION ON ZOOPLANKTON BY PARTICULATE FEEDING FISH

The relationship between the gill raker structure of planktivorous fis h (number, distance between gill rakers and length) and selective feed ing on different species and size classes of zooplankton was studied. Gill raker structure was measured for brown trout Salmo trutta, Arctic charr Salvelinus alpinus, whitefish Coregonus lavaretus, roach Rutilu s rutilus, bleak Alburnus alburnus, and three-spined stickleback Gaste rosteus aculeatus. All species are facultative planktivorous fish and occur commonly in Scandinavian lakes. The effect of gill raker structu re was studied by comparing prey found in fish stomachs with the avail ability of zooplankton from several lakes. Gill raker length and dista nce were significantly correlated with fish length. Although gill rake r structure differed among species, all fish species selected the larg er zooplankters. The minimum size of cladoceran species found in fish stomachs was much smaller than the distance between gill rakers. Despi te great differences in gill raker spacing, the minimum size ingested of Daphnia galeata and Bosmina longispina was similar for all predator s. The hypothesis that small zooplankton are strained and retained by the gill rakers in particulate feeding planktivorous fish, particularl y in salmonids and roach, is rejected. (C) 1995 The Fisheries Society of the British Isles.