Anguillicola crassus (Anguillicoloides crassus)
This nematode infects the Japanese eel, Anguilla japonica. Free-living larvae settle in the substrate to get ingested by an intermadiate host, typically a copepod. Young eels get infected by feeding on infected copepods. Interestingly, when infected copepods are eaten by other fishes, the parasite remains alive and can be transmitted from these paratenic hosts to larger eels feeding on them. In the eel, the parasite migrates to the swim bladder where it sexually produces eggs and causes pathological damages (see Muñoz et al. 2015 and references therein). These eggs then pass through the digestive tract and are released into the water.
Importation of Japanese eels to many places of the world for aquaculture is believed to have facilitated the spillover of A. crassus to native eels (Dangel et al. 2013). Within 30 years, most populations of European eels A. anguilla became infected and the parasite is now specializing to infect its novel host (Weclwaski et al. 2013). This rapid spread to native species is connected to the high plasticity of the parasite's life-cycle. Larval infections have been reported in a range of organisms, including aquatic insects and amphibians (Moravec &Skoríková 1998). Recent evidences suggest that the use of paratenic hosts might be facilitated by hyperparasitism of native parasites by A. crassus (Emde et al. 2013). As a consequence, very few measures can be installed to protect native species from this invader and the spillover continues to cause high mortality in native eel populations (Kirk 2003, Barry et al. 2014).
source for picture:http://web.abo.fi/instut/fisk/Fin/Parasiter/anguillicola.htm
