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Haplorchis pumilio (Trematoda: Heterophyidae) has become widely established around the world because of multiple introductions of its snail hosts, and because of its flexible host requirements at the second-intermediate and definitive levels. Although exotic thiarid snails introduced into North American waters have been previously reported to harbor H. pumilio, metacercariae of H. pumilio have not been reported from native fishes in the continental USA. In this study artificially exposed cyprinids to H. pumilio cercariae from infected snails became infected with the trematode, sometimes lethally, when exposed for only 15 minutes to high cercarial densities. Subsequent collection and examination of fountain darters Etheostoma fonticola, a U.S. federally endangered fish species, and the examination of archived specimens of largemouth bass Micropterus salmoides; the IUCN endangered Dionda diaboli, Gambusia nobilis, Cyprinodon elegans; and IUCN vulnerable Etheostoma grahami from West Texas springs resulted in new host and locality records for H. pumilio metacercarial infections in all species except C. elegans. Metacercariae were found encysted in the connective tissue of the head and at fin insertions. Conversely no integumental or visceral infections were observed, regardless of the fish species or collection locality. It is surmised that Haplorchis pumilio is probably present in many aquatic systems where Melanoides tuberculata and Tarebia granifera have become established, but that the metacercariae have been missed by previous investigators because of their small size and unusual anatomical location. Results from this study suggest that subsequent investigators be on the watch for these metacercariae, and that the anatomical sites typical of the worm (fin insertions, and especially the caudal peduncle) be included in routine necropsy procedures for fishes from such habitats. |
