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E e l s w i m - b l a d d e r n e m a t o d e , Anguillicoloides crassus
Overview
.
Short description of Anguillicoloides crassus, E e l s w i m - b l a d d e r n e m a t o d e
A small parasitic nematode worm, found in the swim bladders of native hosts the
Japanese eel (Anguilla japonica), and in Europe, the European eel (Anguilla anguilla).
Description of Anguillicoloides crassus, Eel swim-bladder nematode status in
GB
The swimbladder nematode is now considered ubiquitous throughout England and
Wales, with one isolated record from Scotland.
Author's name:
Leoni Claire Adams
Last updated:
May 5th, 2011
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H a b i t a t s u m m a r y : Anguillicoloides crassus, E e l s w i m - b l a d d e r n e m a t o d e
This species is normally found in fresh or brackish water, however it has also been
recorded in marine hosts. In Europe, adults are found in the swim bladder of
swimbladder nematode. A number of intermediary stages are found in a variety of
crustacean (ususlly copepod) and fish species.
Overview table
Environment:
Marine and Freshwater
Species status:
Non-Native
Native range:
China, Kazan-retto, Nansei-shoto, Ogasawara-shoto,
Taiwan, Vietnam
Functional
type:
Parasite or parasitoid
Status in
England:
Non-Native
Status in
Scotland:
Non-Native
Status in
Wales:
Non-Native
Location of
first record:
River Welland and River Trent
Date of first
record:
1987
Invasion history: Anguillicoloides crassus, Eel
swim-bladder nematode
Origin
The swimbladder nematode is native to east Asia. The native host of this species is
the Japanese eel (Anguilla japonica), where this species does not cause great concern.
First Record
Recorded in 1987 in the River Welland and River Trent in eastern Enlgand, and the tidal
river Thames.
Pathway and Method
The swimbladder nematode was probably brought into Europe unintentionally through
the import of infected Japanese eels. This species has continued to spread through
wild and farmed populations of the European eel. Spread can mainly be attributed to
transport, via both import and export of infected European eels. In Britain the
distribution of this species corresponds to the routes taken by lorries involved in its
import and export.
Species Status
The swimbladder nematode was first observed in Europe in 1982, found in eel stocks in
northern Germany. Following this it spread rapidly through both farmed and wild
European eel populations throughout Europe. Infection had by 2003 reached Egypt,
Morocco and Tunisia (Kirk, 2003). This species has also now been found in North
America infecting the American eel ( Anguilla rostrata).
Ecology & Habitat: Anguillicoloides crassus, Eel
swim-bladder nematode
Dispersal Mechanisms
The primary dispersal vector for this species appears to be related to the commercial
transport of live eels. In GB infection is highly correlated to the routes taken by lorries
for commercial transportation routes, both involved in import and export. It is believed
that infection is likely to occur during water changes made by lorries. Initial juvenile
stages can survive up to around 80 days in freshwater. In addition eels are a motile
species and as such will allow an additional natural method of dispersal.
Reproduction
Copulation occurs in the lumen of the infected eel's swimbladder. Eggs move from the
swim bladder and enter the water column via the intestine. Motile second stage
juveniles will then be preyed upon by a number of invertebrates including various
species of crustacea, which form intermediate hosts. Within the intermediate host the
larvae will penetrate the gut and enter the body cavity, where they moult into third
stage juveniles. If the intermediate hosts are directly consumed by eels, the third
stage larvae will pass from the gut into the swimbladder, and moult into adult stage. If
the intermediate hosts are eaten by fish, the third-stage juveniles penetrate the wall
of the intestinal tract. Small benthic fish form a significant part of the eels' diet and
large numbers of the swimbladder nematode are transferred in this way.
Known Predators/Herbivores
Early stage juveniles are consumed by crustacean species which in turn may be preyed
upon by eels.
Resistant Stages
None known, but second stage juveniles can survive in the water column and remain
infective to intermediate hosts for up to 80 days in fresh water.
Habitat Occupied in GB
Fresh and brackish water habitats. Found in eel swim bladders and a range of
crustacean and fish species as the hosts of intermediate growth stages.
Distribution: Anguillicoloides crassus, Eel
swim-bladder nematode
The swimbladder nematode is widely distributed in England and Wales, with an isolated
record from Scotland.
I m p a c t s : Anguillicoloides crassus, Eel
swim-bladder nematode
Environmental Impact
The swim bladder nematode is a blood sucking parasite. It's feeding method causes
swim bladder wall inflammation in infected individuals. High levels of infestation can
lead to thickening or rupture of the swimbladder wall. Molnar et al (1991) reported
mass eel mortalities with swimbladders of the dead eels containing 30-50 adult A.
Crassus, thousands of larvae and remnants of dead nematodes. In some eels, the
swimbladder wall was thickened and haemorrhagic. Infection in a population can
reduce growth rate of the eels, increase susceptability to secondary infections and
increase mortality rate. Swimming ability may be impaired which in turn compromises
the eels' ability to complete essential migrations.
Health and Social Impact
None known.
Economic Impact
In eel farms the parasite is a serious problem, leading to decreased growth and
reduced market value of fish. The swim bladder nematode also causes increased
susceptability to secondary infection and mortality, increasing costs to the industry.
References & Links: Anguillicoloides crassus, Eel
swim-bladder nematode
Identification
Evans, D.W. & Matthews, M.A. (1999) Anguillicola crassus (Nematoda,
Dracunculoidea); first documented record of this swimbladder parasite of eels in
Ireland. Journal of Fish Biology, 5 5, 665-668
Biology, ecology, spread, vectors
Kennedy, C. R. and Fitch, D. J. (1990) Colonization, larval survival and epidemiology of
the nematode Anguillicola crassus, parasitic in the eel, Anguilla anguilla, in Britain,
Journal of Fish Biology, 3 6, 117-131.
Pilcher, M. W. and Moore, J. F. (1993) Distribution and prevalence of Anguillicola
crassus in eels from the tidal Thames catchment. Journal of Fish Biology, 4 3, 339-344.
Thomas, K. and Ollevier, F. (1992) Paratentic hosts of the swimbladder nematode
Anguillicola crassus. Diseases of Aquatic Organisms, 1 3, 165-174.
Management and impact
Kirk, R. S. (2003) The impact of Anguillicola crassus on European eels. Fisheries
management and ecology, 1 0, 385-394.
Molnar, K., Szekely, Cs, & Baska, F. (1991) Mass mortality of eel in Lake Balaton due to
Anguillicola crassus infection. Bulletin of the European Association of Fish
Pathologists, 1 1, (6), 211-212.
Sjoberg, N.B., Petersson, E., Wickstrom, H. & Hansson, S. (2009) Effects of the
swimbladder parasite Anguillicola crassus on the migration of European silver eels
Anguilla Anguilla in the Baltic Sea. Journal of Fish Biology, 7 4, 2158-2170
General
Kennedy, C. R. (1993) Introductions, spread and colonization of new localities by fish
helminth and crustacean parasites in the British Isles: a perspective appraisal. Journal
of Fish Biology, 4 3 , 287-301.
Scholz, T. (1999) Parasites in cultured and feral fish. Veterinary Parasitology, 8 4,
317-335.