Infection by Anguillicoloides crassus in a riverine stock of European eel, Anguilla anguilla

Infection by the parasitic nematode Anguillicoloides crassus Kuwahara, Niimi & Itagaki, in a wild riverine stock of European eel, Anguilla anguilla (L.), in a near pristine river was investigated. Samples were collected on a seasonal basis in distinct habitats along the river gradient. This study highlighted the presence of the parasite and completion of the whole life cycle in eels from the Rio Esva. Infection levels by A. crassus were high at three sites between the mid river to the estuary and also varied among seasons. Condition of eels was lower at upstream sites compared with downstream locations. Although high-quality, environmental conditions in the Rio Esva may buffer the effects of A. crassus on eels, potential impacts and limiting factors for the parasite are discussed.