Metacercariae of Haplorchis pumilio (Looss, 1896) in Carassius auratus (Linnaeus, 1758) from Mérida City, Yucatán, Mexico: a co-introduced parasite.
The invasive alien species (IAS) and adult trematode parasite of reptiles, birds and mammals (including humans), Haplorchis pumilio (Looss, 1896), is recorded for the first time from Yucatán state in Mexico. The ornamental freshwater fish species, Carassius auratus ("goldfish") from pet shops from Mérida City, were necropsied to search for parasites. The trematode was identified based on molecular and morphological data of metacercariae collected from seven out of ten pet shops sampled. Partial sequences of the 28S ribosomal and COI mitochondrial genes corroborate the identifications based on morphological characters. DNA sequences from GenBank showed low genetic divergence in both genes from H. pumilio associated with three different host groups during larval and adult stages around the world, e.g., cercariae from Melanoides tuberculata ("red-rimmed melania"), from Trichogaster trichopterus ("three spot gourami") and trematode adults from Homo sapiens. We infer that this trematode was likely introduced by accident through pet shop commerce together with the complex of the IASs, M. tuberculata and C. auratus. As Yucatán is the second major ornamental fish producing state in Mexico, accidental release of these IASs into the aquatic environment could result in the introduction of H. pumilio into regional freshwater bodies. The introduction of H. pumilio in Yucatán is probably relatively recent and due to the paucity of studies directed at this parasite, its distribution is not well known, but since its potential pathogenicity can cause an emergence of diseases, not only in wildlife, but also in local human populations, particular attention should be given to the findings of this study.