Based on light and scanning electron microscopical studies, two new species of nematode parasites are described from freshwater fishes in Thailand: Orientatractis mekongensis n. sp. (Atractidae) from the intestine of Pangasius bocourti Sauvage (type-host) and Helicophagus leptorhynchus Ng & Kottelat (both Pangasiidae, Siluriformes), and Neosynodontisia suratthaniensis n. sp. (Pharyngodonidae) from the intestine of Labiobarbus siamensis (Sauvage) (Cyprinidae, Cypriniformes), for which a new genus Neosynodontisia n. g. is established. Orientatractis mekongensis is mainly characterised by the number and distribution of caudal papillae (2 preanal, 1 adanal and 5 postanal pairs), the length of the left spicule (306-384 µm) and large body sizes (length of males and gravid females 5.4-6.7 mm and 7.8-9.0 mm, respectively). Neosynodontisia differs from other pharyngodonid genera with representatives parasitic in fishes not only by some morphological features (mouth withdrawn into the cephalic end with inflated cuticle, structure of the male caudal end, filamented eggs), but mainly by the occurrence of males inside the body of females. A key to the genera of the Pharyngodonidae with representatives parasitising fishes is provided.

• MeSH
• Species Specificity MeSH
• Nematoda anatomy & histology   classification   ultrastructure   MeSH
• Microscopy, Electron, Scanning MeSH
• Fresh Water MeSH
• Catfishes parasitology   MeSH
• Animals MeSH
• Check Tag
• Male MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Geographicals
• Thailand MeSH

For the first time, the nematode Rhabdochona kidderi kidderi Pearse, 1936 (Rhabdochonidae) was recorded from fishes of the Lacantún River (Usumacinta River basin) in the Lacandon rain forest, Chiapas State, southern Mexico. Amphilophus nourissati (Allgayer) and Theraps irregularis Günther (both Perciformes: Cichlidae) were found to be the only definitive hosts in the locality, whereas Eugerres mexicanus (Steindachner) (Perciformes: Gerreidae), Ariopsis sp., Cathorops aguadulce (Meek) and Potomarius nelsoni (Evermann & Goldsborough) (all Siluriformes: Ariidae), Ictalurus furcatus (Valenciennes) (Siluriformes: Ictaluridae) and Strongylura hubbsi Collette (Beloniformes: Belonidae) all harboured the nematode's fourth-stage larva and only served as paratenic hosts. All these fish species represent new host records for this parasite. The morphology of both adults and larvae was studied in detail by light and scanning electron microscopy, and some conspecific museum specimens from three other host species were also examined for comparison. Rhabdochona ictaluri Aguilar-Aguilar, Rosas-Valdez & Pérez-Ponce de León, 2010 is considered here to be a junior synonym of R. kidderi kidderi. A high degree of the variability of some morphological and biometrical features (deirid shape, left spicule length) and an unusually wide range of hosts suggest that R. kidderi may represent a species complex, but further studies are necessary in this respect. A key to Rhabdochona species and subspecies occurring in Mexico is provided.

• MeSH
• Species Specificity MeSH
• Nematoda classification   ultrastructure   MeSH
• Host-Parasite Interactions * MeSH
• Larva MeSH
• Microscopy, Electron, Scanning MeSH
• Nematode Infections parasitology   veterinary   MeSH
• Fish Diseases parasitology   MeSH
• Rivers * MeSH
• Fishes MeSH
• Trees * MeSH
• Animals MeSH
• Check Tag
• Male MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Geographicals
• Mexico MeSH