DIETARY PREFERENCE OF THREE FRESHWATER GASTROPODS FOR EIGHT NATURAL FOODS OF DIFFERENT ENERGETIC CONTENT

摘要

The food preferences of three freshwater gastropods, Radix peregra (Pulmonata), Bithynia tentaculata and Bythinella dunkeri (Prosobranchia), have been examined in laboratory experiments. Eight natural foods, a green alga, a cyanobacterium, and leaves of sycamore maple, alder and oak with different conditionings, were tested in various combinations. The number of animals found on these foods during a three-hour period was counted. There were significant differences in the food choice of the three species: Bithynia tentaculata clearly preferred algae and cyanobacteria, Bythinella dunkeri selected leaves conditioned by microorganisms and discriminated against unconditioned leaves and algae, and Radix peregra showed intermediate food preferences for almost all foods. For Radix and Bithynia, the results of these experiments were correlated with the C:N ratio and the % nitrogen content of the food items: preference increased with decreasing C:N ratios and with increasing nitrogen content. There was no such correlation for Bythinella. The possible reasons for this are discussed.