Thirty species (approximately 350 specimens) of freshwater ornamental fishes imported into the Czech Republic from Southeast Asian farms were examined for monogeneans during 2001 – 2003. The survey revealed the presence of 7 previously described and 6 new monogenean species on the gills of 13 host species. Bychowskyella tchangi Gussev, 1976 was reported from Clarias batrachus; Dactylogyrus anchoratus (Dujardin, 1845), D. formosus Kulwiec, 1927, D. intermedius Wagener, 1910 and D. vastator Nybelin, 1924 from Carassius auratus; Dactylogyrus sp. 1, Dactylogyrus sp. 2 and Dactylogyrus sp. 3 from Balantiocheilos melanopterus; Heteronchocleidus buschkieli Bychowsky, 1957 from Betta splendens, Trichopsis schalleri; Mastacembelocleidus bam (Tripathi, 1959) from Macrognathus siamensis and M. circumcinctus (new host records); Thaparocleidus siamensis (Lim, 1990) and Thaparocleidus caecus (Mizelle et Kritsky, 1969) from Pangasius hypophthalmus; Thylacicleidus brunensis n. sp. from Tetraodon biocellatus, Thylacicleidus latus n. sp. and T. serendipitus Wheeler et Klassen, 1987 from Tetraodon nigroviridis; Trianchoratus acleithrium Price et Berry, 1966 from Trichogaster trichopterus and Helostoma temminckii; Vancleaveus sp. from Pseudoplatystoma fasciatum. The only monogeneans recorded from the external surfaces of the examined fish were post-larval stages of Thylacicleidus spp. from tetraodontids. The most heavily infested fish (prevalence = 100%; intensity = more than 500 specimens/fish) were Pangasius hypophthalmus infected with Thaparocleidus caecus, Tetraodon biocellatus with Thylacicleidus brunensis and Tetraodon nigroviridis with Thylacicleidus latus. Histological examination of the gills from tetraodontids revealed only minor histopathological changes, however, it showed differences in the adhesive attitude between Thylacicleidus latus and T. serendipitus on the gills of Tetraodon nigroviridis. In Pangasius hypophthalmus, Thaparocleidus caecus and T. siamensis caused hyperplasia and metaplasia of the lamellar epithelial cells. My participation at ISM5 was supported by the Research Project of Masaryk University, MSM 0021622416.