Relationship between Body Size of the Rotifer Brachionus plicatilis and the Minimum Size of Particles Ingested

Abstract

The minimum size of particles ingested by Brachionus plicatilis was determined by the use of an automatic blood cell counter. Dividing the size distribution of baker’s yeast into 12 sections (2.87-5.30 μmϕ), the minimum one among those sections where particles decreased as the result of ingestion was denoted as Smin. After calculating the ingestion rates (I8) and (I) respectively in Smin and the uppermost section where particles were large enough to be ingested by any individual, the percentage of rotifers which could ingest even Smiewas presumed from the ratio (Is/I). On the assumption that the smaller individuals can ingest the smaller particles, the one corresponding to (Is/I)% on the ogive of rotifer size may have ingested the smallest particle whose diameter was the upper end of Smin. A regression line Y=0.01082IX+1.8958 (r=0.61) was obtained, where Y is the diameter of the smallest particle which can be ingested by the individual whose lorica length is X μm. The reason for the low correlation rate is explained by the result of the measurement of a masticatory organ. The size of jaw in the mastax, which may regulate the ability of mastification, is uniform irrespective of rotifer size. © 1984, The Japanese Society of Fisheries Science. All rights reserved.