Abstract
For this study 29 species of fresh-water fishes have been examined on sessiline ciliates. From O. Peritricha 33 species have been found (27 from Genus Apiosoma, 3 from Genus Epistylis and 1 from Genus Pyxidiella), 18 of them are new species. A new key for the determination of Apiosoma-species is given. From O. Suctoria Trichophrya piscium is described. Besides ecological factors the relation between Apiosoma-species and carrying animal is examined. Apiosoma-species are never parasites.