A serological study of prey selection by Nephelopsis obscura Verrill (Hirudinoidea)

Abstract

The prey range of Nephelopsis obscura was determined in three limnologically similar field sites using a serological technique. At each site the relative magnitude of utilization from highest to lowest was Chironomidae, Oligochaeta, Amphipoda, Copepoda–Cladocera, and Gastropoda respectively. When the three sites were compared, the relative proportions of these prey categories were shown to differ. Feeding activity was highest in the spring and summer and lowest in the fall and winter. Within each weight class of N. obscura, the Chironomidae, Amphipoda, and Oligochaeta were eaten most frequently. The Gastropoda and Copepoda–Cladocera were preyed upon more intensely by the smaller weight classes. The smaller (0–30 mg) and the larger (180−200+ mg) weight classes displayed proportionately higher feeding activity than the intermediate weight classes. Site-specific differences in weight class utilization of prey were recorded, indicating that generalizations on feeding activity of N. obscura are difficult to make even in similar field sites located in the same geographical area.