Onchocleidus principalis (Monogenea: Ancyrocephalidae) Co-introduced to Europe with Centrarchid Fish

Non-native parasites are often translocated into novel areas together with their natural hosts, but the parasite diversity is frequently lower compared to the host's native range.

This paper provides morphological and molecular characterisation for non-native monogenean parasite Onchocleidus principalis (Ancyrocephalidae) co-introduced with its fish host to Portugal, Europe, including new details on the species' vaginal morphology and metrics.

Two host species, the largemouth bass Micropterus salmoides and pumpkinseed sunfish Lepomis gibbosus, were sampled from two reservoirs (Landeira, Coruche) in the Atlantic Sea drainage. Morphometric analysis and sequencing of 28S rDNA were performed.

Presence of O. principalis was confirmed in all individuals of largemouth bass. Accidental findings on pumpkinseed sunfish at both sampling sites represent new host records for this parasite species. The morphometric description of O. principalis showed high similarity to the species in its native range. No intraspecific sequence variation of partial 28S rDNA was observed between specimens from the two sampling sites. Presence of another North-American ancyrocephalid parasite Onchocleidus dispar was confirmed in pumpkinseed sunfish at both sites, and in largemouth bass from the Coruche Reservoir, this representing the first record of O. dispar on largemouth bass in Europe.

Onchocleidus principalis has been confirmed to parasitise both centrarchid fish species introduced to Europe. Compared to other studies, the species collected in Portugal exhibits pronounced vaginal armament.