Prevalence of fish-borne trematodes of the family Heterophyidae at Pasak Cholasid Reservoir, Thailand.

The prevalence of fish-borne trematodes was investigated in various species of freshwater fish at Pasak Cholasid Reservoir in Thailand. The samples were collected from fish markets around the reservoir between June 2011 and May 2012. A total of 789 fish samples were classified into 25 species. The metacercariae (i.e., the larval stage of trematodes) were examined from 4 parts of the fish body, and evaluated using the compression method. Ten species from two families of the fish collected were found to have trematodes of various infection rates. Among the Cyprinidae there were 9 species: Barbonymus altus (100%; 14/14), Barbonymus schwanenfeldii (88.71%; 55/62), Cyclocheilichthys enoplos (49.53%; 53/107), Hampala dispar (66.67%; 6/9), Henicorhynchus siamensis (23.36%; 25/107), Hypsibarbus wetmorei (85.29%; 58/68), Labiobarbus siamensis (77.78%; 56/72), Osteochilus hasseltii (16.28%; 7/43), and Puntioplites proctozysron (53.97%; 34/63). Among the Eleotridae, only one species Oxyeleotris marmorata was found with an infection rate of 20% (2/10). Based on morphological features and corroborated by molecular genetic data, the fish trematodes were found to represent two species of the Heterophyidae, viz. Haplorchis pumilio and Centrocestus formosanus. Thus, it is evident that freshwater fish from the Pasak Cholasid Reservoir exhibit heterophyid trematode infections.