Trematode metacercariae and adults in cyprinoid fish from Khun Thale Swamp in Surat Thani province, Thailand.

The present study aimed to determine the infection status of trematode metacercariae and adults in cyprinoid fish from the Khun Thale Swamp in Surat Thani, Southern Thailand, with epidemiologic and faunistic viewpoints. In 2020, 577 fish in 15 species were collected in the summer (February-April) and rainy (September-November) seasons. Fish were individually examined for trematode metacercariae in the whole body and adults in the gastrointestinal tract using a stereomicroscope. Three species of digenetic trematode metacercariae, i.e., Haplorchis taichui, Haplorchoides mehrai, and Centrocestus formosanus, were detected in the muscle, fin, and/or scale of fish. Two species of adult flukes, including Rohdella siamensis and Helostomatis cyprinorum, were collected in the intestines. The prevalence of overall trematode infections was 32.4% (187/577 fish), which was higher in the rainy season (41.4%; 118/285) than in the summer season (23.6%; 69/292). The metacercariae of H. taichui and H. mehrai were detected in 7 fish species each, and those of C. formosanus were found only in Rasbora toneri. The aspidogastrean trematode R. siamensis (adult) was detected in Babonymus gonionotus. A digenean species, H. cyprinorum (adult), was found in Labiobarbus siamensis and Osteochilus vittatus. The present study has first confirmed that the metacercariae of heterophyid flukes, including H. taichui, H. mehrai, and C. formosanus, and adults of R. siamensis (Aspidogastrea) and H. cyprinorum (Digenea) are infected in some species of the cyprinoid fish from the Khun Thale Swamp in Surat Thani, Thailand.

Morphological and Molecular Characterization of Haplorchoides Mehrai Pande and Shukla 1976 (Digenea: Heterophyidae) from Chiang Mai Province.

Cyprinoid fish in Chiang Mai province has been reported the presence of a large number of metacercariae, particularly the metacercariae of Haplorchoides and those not identified to species. This study aims to investigate morphological and molecular characteristic of the minute intestinal fluke H. mehrai metacercariae in two cyprinoid fish species from Chom Thong district, Chiang Mai province, Thailand: the Tinfoil barb (Barbonymus schwanenfeldii) and the White eye barb (Cyclocheilichthys repasson). A total of 180 fish (90 from B. schwanenfeldii and 90 from C. repasson) were collected over three seasons: cool, hot and the rainy season (December 2015 to August 2016). Fish were examined for H. mehrai metacercariae infection, including areas such as muscle and the inner side of body scales, by using a light microscope. The prevalence of H. mehrai metacercariae in B. schwanenfeldii and C. repasson was 73.33 % and 100 % respectively. Haplorchoides metacercariae were identified as H. mehrai based on the morphological characteristics; the position of the acetabulum and the number and arrangement of the acetabular spines. Phylogenetic analysis based on Cytochrome c Oxidase subunit I (COI) gene showed that H. mehrai metacercariae from B. schwanenfeldii and C. repasson were the same species as the adult stage of H. mehrai from Hemibagrus nemurus and Mystus multiradiatus. Both morphological and molecular characteristic could indicate that Haplorchoides metacercariae originated from this study were H. mehrai. Furthermore, it is a new record of the minute intestinal fluke Haplorchoides mehrai in Chiang Mai Province.

New locality record for Haplorchoides mehrai and possible interactions with Opisthorchis viverrini metacercariae in cyprinid fishes in Northeast Thailand.

Metacercariae of Opisthorchis viverrini, a carcinogenic liver fluke, and Haplorchoides sp., a trematode maturing in catfish, are commonly found in cyprinid fish, the second intermediate hosts of both flukes. However, the specific identity of Haplorchoides sp. in Thailand and a precise assessment of the effects of co-infections with O. viverrini have never been clarified. Therefore, we aimed to identify the species of Haplorchoides and to investigate possible interactions of the two trematode species in cyprinid fishes. Based on the morphology and morphometry of the cercaria, metacercaria, and adult stages, the Haplorchoides species found was identified as Haplorchoides mehrai Pande and Shukla 1976. Thailand is formally recorded as a new locality for H. mehrai, where naturally infected hosts include the snail Melanoides tuberculata (first intermediate host), the cyprinid fishes Hampala dispar, Cyclocheilichthys apogon, Puntius leiacanthus, Labiobarbus burmanicus, and Cirrhina jullieni (second intermediate hosts), and a catfish, Mystus nemurus (definitive host). The co-infection rates of O. viverrini and H. mehrai were significantly associated with fish species and fish body region (P < 0.001), with an overall significantly higher average intensity of H. mehrai (126.26 metacercariae/fish) than that of O. viverrini (18.02 metacercariae/fish). Further work is required to demonstrate the extent and mechanisms of possible interactions between these trematode species in the fish host. These data may provide a better understanding of O. viverrini transmission dynamics, and help design integrated control interventions.