Prevalence of trematode metacercariae in cyprinoid fish of Ban Pao district, Chiang Mai Province, northern Thailand.
Fish (n=699) were collected from both man-made water reservoirs and natural sources in Ban Pao district, Chiang Mai Province, northern Thailand, from July 1996-May 1997. Ten species of cyprinoid fish were identified (Puntius leiacanthus, P. gonionotus, P. orphoides, Thynnichthys thynnoides, Danio regina, Puntioplites proctozysron, Hampala macrolepidota, Aplocheilus panchax, Lariobarbus burmanicus and Tilapia nilotica [Oreochromis niloticus]) and all but T. nilotica harboured metacercariae (of Opisthorchis viverrini and small intestinal flukes of the family Heterophyidae: Haplorchis taichui, H. pumilio and Centrocestus spp.). Metacercariae of H. taichui (n=34 169) were 384 times more common than those of O. viverrini (n=89). Among the fish collected, Puntius leiacanthus harboured the highest number of metacercariae of H. taichui (182 metacercariae/fish) and P. orphoides harboured the highest number of metacercariae of O. viverrini (1.4 metacercariae/fish). Metacercariae of H. taichui occurred all year-round, with the highest and lowest prevalences in winter and the rainy season, respectively.