A total of 201 specimens of crucian carp (Carassius auratus auratus (Linnaeus, 1758)), including 64
from swamp Bau Sung (Tuy An District), 55 from Ky Lo River (Tuy An District) and 82 from freshwater fi sh
ponds (Hoa Xuan Dong- Dong Hoa District) of Phu Yen Province were used for studying of the compositions,
prevalences and intensities of Monogeneans. Results showed that, crucian carp in Phu Yen was infected with
6 Monogenean species, including Dactylogyrus anchoratus (Dojardin, 1845) Wagener, 1857, Dactylogyrus
formosus Kulwieć, 1927, Dactylogyrus intermedius Wegener, 1909, Dactylogyrus vastator Nybelin, 1924,
Gyrodactylus hronosus Zitnan, 1964, and Eudiplozoon nipponicum (Goto, 1891)). Of which, fi sh collected
from Bau Sung Swamp was infected with 6 Monogenean species, fi sh from Ky Lo River was infected with 5
Monogenean species (not infected with D. anchoratus), fi sh from freshwater fi sh ponds was infected with 4
Monogenean species (not infected with D. anchoratus and E. nipponicum). The prevalences and intensities are highest on fi sh from freshwater fi sh ponds, while they were not much different between fi sh collected from Bau Sung Swamp and Ky Lo River.