Anguillicola crassus

Phylum: Nematoda
Class: Dracunculoidea
Order: Anguillicolidae
Species name: Anguillicola crassus  Kuwahara, Niimi & Itagaki 1974
Synonyms: None
Common name: Swim-bladder nematode
Date of introduction and origin
Anguillicola crassus was introduced to the European continent in the 1980s, where it was reported independently from Germany and Italy in 1982, having been introduced from East Asia (Koops & Hartmann 1989). It was introduced to England in 1987 (Kennedy & Fitch 1990) from continental Europe (Køie 1988).
Method of introduction
It was imported with infected Japanese eels Anguilla japonica into Europe; and with continental Anguilla anguilla to Britain.
Reasons for success
A variety of crustacean intermediate hosts and fish parasitic hosts are known for this parasitic swim-bladder nematode, increasing the chances of its survival. There is high resistance of the sheathed, second stage, larvae to adverse conditions (Kennedy & Fitch 1990), and the species showed an excellent colonising ability (Kennedy 1993). An absence of native swim-bladder nematodes is also a factor in the success of A. crassus as there is a lack of competitors and resistance of the host.
Rate of spread and methods involved
Once introduced into a lake or river, Anguillicola crassus may spread rapidly among the eel population. Levels of infestation have been recorded to rise from 10% to 50% within a year (Belpaire et al. 1989; Koops & Hartmann 1989). Spread within an aquatic system is generally through intermediate hosts and movements of other fish. Spread between localities is generally through transport of infected eels. A. crassus has been recorded in the open sea and in brackish coastal localities (Koops & Hartmann 1989; Mellergaard 1988). C.R. Kennedy (pers. comm.) has found it in lagoons in Italy at salinities up to 20%o.
It is widespread in England, although not yet found in Scotland and Wales (Ashorth 1995). It is now found in most European countries (except Ireland) including in the Baltic Sea (Kennedy & Fitch 1990) and Iceland.
Factors likely to influence spread and distribution
Uncontrolled movement of infected eels will aid its spread.
Effects on the environment
Common eels Anguilla anguilla, if infected by Anguillicola crassus, can show adverse effects if the level of infestation is high. These include higher susceptibility to bacterial infections and death. The wall of the swim bladder may thicken and inflammation occur. Growth may slow and damage to the swim bladder may prevent the spawning migration to the western Atlantic (Køie 1988). Kennedy & Fitch (1990) document the occurrence of these effects in eels in British waters.
Effects on commercial interests
In eel farms the parasites have been observed to cause reduction in growth rate. The wall of the swim bladder of highly infected eels may burst (Mellergaard 1988).
Control methods used and effectiveness
No information is available.
Beneficial effects
None known.
This species is normally found in freshwater conditions, and brackish waters up to 20‰ salinity. However, it has been recorded in hosts in the open sea.
Ashorth, S.T. 1995. The dynamics and regulation of Anguillicola crassus (Nematoda) populations in the European eel (Anguilla anguilla). Doctoral Thesis, University of Exeter.
Belpaire, C., De Charleroy, D., Thomas, K., van Damme, P., & Ollevier, F. 1989. Effects of eel restocking on the distribution of the nematode Anguillicola crassus in Flanders, Belgium. Journal of Applied Ecology, 5: 151-153.
Kennedy, C.R. 1993. Introductions, spread and colonization of new localities by fish helminth and crustacean parasites in the British Isles: a perspective and appraisal. Journal of Fish Biology, 43: 287-301.
Kennedy, C.R., & Fitch, D.J. 1990. Colonisation, larval survival, and epidemiology of the nematode Anguillicola crassus, parasite in the eel Anguilla anguilla in Britain. Journal of Fish Biology, 36: 117-131.
Koops, H., & Hartmann, F. 1989. Anguillicola infestations in Germany and in German eel imports. Journal of Applied Ichthyology, 1: 41-45.
Køie, M. 1988. The swim bladder nematodes Anguillicola spp. and the gill monogeneans Pseudodactylogyrus spp. in European eels.In: Case histories of effects of introducing and transfers on marine ecosystems. Proceedings of ICES mini-symposium. Bergen, Norway, October 1988.
Mellergaard, S. 1988 Ålens svømmeblæreorm Anguillicola - en ny parasit i den Europæiske ålebestand. Nordiske Aquacultur, 4: 50-54.
Thomas, K. 1993. The life cycle of the eel parasite Anguillicola crassus (Nematoda: Dracunculoidea). Doctoral Thesis, Katholieke Universiteit Leuven.
Acknowledgements (contributions from questionnaire)
Professor C.R. Kennedy, University of Exeter.