DIEL FEEDING PERIODICITY IN LARVAE OF THE VENDACE (COREGONUS-ALBULA L.) AND INFLUENCE OF FOOD AVAILABILITY AND ENVIRONMENTAL-FACTORS ON FOOD-INTAKE

Samples were taken every 2 h for 10 days to determine diel foraging pe riodicity of vendace larvae in the littoral zone of Lake Lentua, north ern Finland and to assess environmental factors affecting food intake. Feeding was associated with daylight conditions, so feeding ceased in the dark. Soft-bodied, rapidly digested rotatorians indicated the per iodicity more clearly than hard-shelled prey such as cladocerans and c opepodites. Wind events and waves in the littoral zone were the major factors affecting food abundance and feeding by the larvae. Waves indu ced by strong inshore winds reduced zooplankton density, increasing th e occurence of larvae with empty guts to 80%. Reduced food availabilit y was reflected in the guts of larvae within 6 h. The density of suita bly-sized zooplankton, together with wind effects and photoperiodism, explained most of the variation in gut content in the larvae.