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

摘要

The relationship between the gill raker structure of planktivorous fish (number, distance between gill rakers and length) and selective feeding 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 Rutilus rutilus, bleak Alburnus alburnus, and three-spined stickleback Gasterosteus aculeatus. All species are facultative planktivorous fish and occur commonly in Scandinavian lakes. The effect of gill raker structure was studied by comparing prey found in fish stomachs with the availability of zooplankton from several lakes. Gill raker length and distance were significantly correlated with fish length. Although gill raker structure differed among species, all fish species selected the larger zooplankters. The minimum size of cladoceran species found in fish stomachs was much smaller than the distance between gill rakers. Despite great differences in gill raker spacing, the minimum size ingested of Daphnia galeata and Bosmina longispina was similar for all predators. The hypothesis that small zooplankton are strained and retained by the gill rakers in particulate feeding planktivorous fish, particularly in salmonids and roach, is rejected. (C) 1995 The Fisheries Society of the British Isles.