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
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
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.
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:
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:
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.