EN
To determine the way of nutrition in Ergasilus sieboldi Nordmann parasiting on tench gills, the author used histologic sections to analyse the content of alimentary tracts. Apart from the granulations encountered in the secretion of the digestive glands, 21 intestines (total number of parasites under investigation was 69) contained large accumulations of cells, amounting even to 80; they were mostly well-preserved connective tissue cells, nuclei of cells of branchial epithelium and erythrocytes. The observations corroborate the deleterious action of Ergasilus sieboldi which is mostly due to its intensive feeding on the cells of branchial tissue of the host.