Eel Swim bladder Nematode Anguillicola crassus
Adult nematodes of Anguillicola crassus can be found in the swim bladder of the European eel (Anguilla anguilla) and the American eel (A. rostrata). Infection can increase bacterial infection rates and eel mortality and may be contributing to the dramatic decline in European eel populations by impeding spawning success.
This endoparasite is native to Southeast Asia and its native host is the Japanese eel (A. japonicas). Planktonic crustaceans act as intermediate hosts. It reaches maturity when the crustaceans are consumed by eels allowing the parasite to burrow through the gut and lodge in the swim bladder. A. crassus has spread throughout Europe since its arrival in Germany and Italy in 1982. Likely vectors of infection include stocking of eels and the expulsion of ballast water from ships which can carry infected crustacean hosts. Once introduced to a population the nematode can spread rapidly, infecting between 10 and 50% of the population within a year. This species bears many attributes of a highly invasive species as it is highly fertile, reproduces rapidly and has a long lived free-living larval stage. The second stage larvae is also highly resilient to adverse conditions. It can survive in fresh and brackish waters and some infected eels have been recorded in the open sea.
It has been estimated that Anguillicoides crasssus is present in at least 70% of Ireland’s wetted area and is spreading. IFI are examining the extent of A crassus distribution using the eel monitoring programme together with the water framework directive surveys. For more information on the project see here.