Abstract Fish eustrongylidosis is a parasitic disease involving 3 rd and 4 th stages larvae of the Eustrongylides nematode (Ph: Nemathelminthes). Over the past 20 years, the number of case reportings on fish eustrongylidosis has increased, especially within industrial fisheries and amongst fishermen. Recent data have confirmed the tendency of a spatial extension of the parasite distribution area towards the Danubian shores of Oltenia and Calarasi, as well as a progressive increase of affected fish host species into natural environments. During the study, the infested fish underwent parasitological and anatomopathological examinations, with the aim to identify the nematode (genus level) and the pathological effects of the parasite over its host. In Romania, this is the first report on eustrongylidosis in eel, detected within fish populations inhabiting some Danubian Delta lakes. This case comes to confirm the low host specificity characteristics of this parasite and its spreading tendency towards new environments.