For many years his research activity has been oriented mainly to studies of the biology, ecology and taxonomy of helminth parasites of fishes and some other vertebrates, where he has achieved many priority results; he has broad international co-operations. He himself worked in many countries. He published about 350 scientific papers, including 11 books. He was an organizer or a co-organizer of two international symposia on fish parasites, three international ichthyoparasitological training courses and the International Workshop on Anguillicolosis of Eels. He has been the supervisor of several Czech and foreign Ph.D. students. He is a member of editorial boards of two domestic and three foreign international scientific journals, of various professional commissions and domestic and foreign scientific societies.