Parasite surveys and environmental management for prevention of parasitic infection in cultivated Barbonymus gonionotus (Cyprinidae) in fishponds, in an opisthorchiasis endemic area of northeast Thailand

Abstract Snails and fishes from ponds in an area endemic for human liver fluke ( Opisthorchis viverrini ) in Khon Kaen Province, northeast Thailand, were surveyed for the presence of zoonotic helminth parasites during May–November 2007. The surveys were performed to obtain information on the potential for transmission of these parasites to fish cultivated for human consumption. Sixteen species/subspecies of snails from 7 families and 14 species of fish from 6 families were collected for parasitological examination. Four species of snails were found to be infected with a range of trematode species. Bithynia siamensis goniomphalos , the first intermediate host of O. viverrini , was the most commonly infected with trematodes, with a prevalence of infection of 1.69–25.00% in 10 ponds. O. viverrini was found in 1 of 1065 (0.09%) B. siamensis goniomphalos individuals examined in one pond. Metacercariae of Echinostoma revolutum , another agent of human infection, was found in the snail Idiopoma umbilicata in one pond. The fish Luciosoma bleekeri was infected with the trematode Centrocestus caninus in one pond. An environmental management trial was conducted in selected ponds in the endemic area to measure the effects of exclusion of snails and thus trematode parasites. After modifications to the ponds and boundaries, including the exclusion of snails, the ponds were stocked with Barbonymus gonionotus fingerlings. Batches of the fingerlings from the same nursery farm were determined to be free of parasites prior to their introduction to the ponds. The experimental ponds were examined monthly for the presence of snails. Fish were also sampled monthly for parasites. After 8 months, fish grown in environmentally managed ponds were larger than those of the control pond. However, fish in all ponds were found to be infected with the trematode Haplorchis taichui . The source of this zoonotic species is uncertain and will require further investigation and potential environmental management, both at farms and at hatcheries.