The Utilization of Minute food Particles by Goldfish

Abstract

Previous expts. have indicated that fishes living in homotypically conditioned water derive beneficial effects from small regurgitated food particles. The present study centered on an attempt to determine the minimum effective size for such particles. While dilute solutions or suspensions of casein derivatives, milk, egg albumen, etc., had no demonstrable effect on the maintenance of fasting goldfish, suspensions of Escherichia coli and of cooked, filtered soybean meal not exceeding a particle diameter of 5u when present in concns. of 25 mg. had some sustenance value for goldfish not given other food. Results from the use of the alga Chlorella (diam. 12u) in concns. of about 50 mg./l. suggested that positive growth was possible with this as the sole source of food. In no case were suspensions as effective as the same food material in larger aggregates. Certain relations to Putter''s theory of the nutrition of aquatic animals are discussed. The mechanism of in-gestion of these minute food particles may be explained by previously published evidence indicating that these fish normally swallow some of the medium that they inhabit, and therefore also any food substances contained therein.