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Anguillicoloides crassus

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Datasheet

Anguillicoloides crassus

Summary

  • Last modified
  • 14 July 2018
  • Datasheet Type(s)
  • Invasive Species
  • Natural Enemy
  • Preferred Scientific Name
  • Anguillicoloides crassus
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Metazoa
  •     Phylum: Nematoda
  •       Class: Secernentea
  •         Subclass: Spiruria
  • Summary of Invasiveness
  • A. crassus is native to eastern Asia where it is a widespread, non-pathogenic parasite of the swimbladder of Anguilla japonica. Introduced to Germany with imported Japanese eels around 1980, it transferred...

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Pictures

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PictureTitleCaptionCopyright
Anguillicola crassus; nematodes in body cavity, Lough Derg, Ireland.
TitleNematodes in body cavity
CaptionAnguillicola crassus; nematodes in body cavity, Lough Derg, Ireland.
CopyrightDan Minchin
Anguillicola crassus; nematodes in body cavity, Lough Derg, Ireland.
Nematodes in body cavityAnguillicola crassus; nematodes in body cavity, Lough Derg, Ireland.Dan Minchin
Anguillicola crassus; isolated nematodes from eels on Lough Derg, Ireland.
TitleIsolated nematodes
CaptionAnguillicola crassus; isolated nematodes from eels on Lough Derg, Ireland.
CopyrightDan Minchin
Anguillicola crassus; isolated nematodes from eels on Lough Derg, Ireland.
Isolated nematodesAnguillicola crassus; isolated nematodes from eels on Lough Derg, Ireland.Dan Minchin

Identity

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Preferred Scientific Name

  • Anguillicoloides crassus (Kuwahara, Niimi et Itagaki, 1974)

Other Scientific Names

  • Anguillicola crassus Kuwahara, Niimi et Itagaki, 1974

International Common Names

  • English: anguillicolosis; swim bladder worm; swimming bladder worm

Local Common Names

  • Denmark: svømmeblæreorm
  • Germany: Schwimmblasenwurm
  • Netherlands: zwemblaasworm
  • Poland: angwilikola
  • Sweden: simblåsemask

Summary of Invasiveness

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A. crassus is native to eastern Asia where it is a widespread, non-pathogenic parasite of the swimbladder of Anguilla japonica. Introduced to Germany with imported Japanese eels around 1980, it transferred to the European eel Anguilla anguilla and has subsequently spread throughout Europe and northern Africa. Following introduction to America, in less than 20 years it has spread from Texas to Cape Breton in Anguilla rostrata. It has the attributes of an excellent coloniser, including high fecundity, low intermediate host specificity and the ability to use a wide range of freshwater fish as paratenic hosts. These, and the uncontrolled transfers of live eels by man, have facilitated its spread and made it the most invasive helminth known. It can be highly pathogenic to Atlantic eels, damaging swimbladders and able to cause mortalities. It affects eels’ swimming abilities and it is feared that it reduces their ability to migrate to their marine spawning grounds.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Metazoa
  •         Phylum: Nematoda
  •             Class: Secernentea
  •                 Subclass: Spiruria
  •                     Order: Camallanida
  •                         Suborder: Camallanina
  •                             Family: Anguillicolidae
  •                                 Genus: Anguillicoloides
  •                                     Species: Anguillicoloides crassus

Notes on Taxonomy and Nomenclature

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The superfamily Anguillicoloidea contains only one family, Anguillicolidae Yamaguti, 1935. This is now considered (Moravec, 2006) to contain two genera, Anguillicola with a single species and Anguillicoloides with four species. Anguillicoloides crassus (Kuwahara, Niimi et Itagaki, 1974) Moravec and Taraschewski, 1988 is thus the correct nomenclature for the species that has hitherto, and in the great majority of the literature until recently, been referred to as Anguillicola crassus.

Adults of all five species are parasitic in the swim bladders of eels of the genus Anguilla. The preferred host of each is a species of Pacific eel and their heartland and the original area of their distribution is in Asia and Africa, i.e. in countries bordered by the Pacific and Indian oceans. Thus, Anguillicola globiceps Yamaguti, 1935 is a parasite of Anguillajaponica and its native distribution is in China and Japan. A. crassus is probably widespread throughout China, Japan and Korea and its preferred host there is also Anguilla japonica, but Moravec (2006) believes that it may have been introduced into Japan with imports of eels and that its region of origin is elsewhere in the Pacific. The antipodean species Anguillicoloides australiensis (Johnston and Mawson, 1940) Moravec and Taraschewski, 1988 is restricted to Australia and (probably) New Zealand, and infects the long-finned eels Anguilla reinhardtii and, probably, Anguilla dieffenbachii. The other antipodean species, Anguillicoloides novaezelandiae Moravec and Taraschewski, 1988, is a native of New Zealand but also occurs in Australia, and it infects the short-finned eel Anguilla australis. The remaining species, Anguillicoloides papernai Moravec and Taraschewski, 1988, is a native of South Africa and infects the African long-finned eel Anguilla mossambica. It would seem possible that there may be other species in the genus still to be described which infect other species of Pacific eels, but the parasite fauna of these species is still very poorly known. There are no species of anguillicolid native to the Atlantic eels Anguilla anguilla and Anguilla rostrata.
 
In the past there has been considerable confusion in identification of the species, due only in part to inadequate descriptions. This has now been rectified by the full descriptions of each species and the provision of keys (Moravec and Taraschewski, 1988; Moravec, 1994, 2006). Confusion has also arisen in part because two species, Anguillicoloides novaezelandiae and Anguillicoloides crassus,have been introduced into Europe with their natural eel hosts. In 1982, Anguillicoloides novaezelandiae was identified erroneously as Anguillicoloides australiensis in eels Anguilla anguilla in Bracciano lake in Italy (Paggi et al., 1982). The species is still present in the lake but appears to be being replaced there by Anguillicoloides crassus (Moravec et al., 1994a). Although it is now believed that all other records of Anguillicoloides from Europe refer to Anguillicoloides crassus, at the time of its first appearance on this continent there was some confusion with Anguillicola globiceps. However, Taraschewski et al. (1987) have confirmed that the specimens in Germany and Japan do belong to the same species. It is highly likely that Anguillicola globiceps has been introduced into Europe with Pacific eels but there is no record of its having established itself on this continent.

Diseases Table

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Distribution

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It would appear that A. crassus was originally restricted to East Asia throughout which it is probably widespread and endemic, especially in China, Japan, Korea and Taiwan (there are not many records of its being definitely identified in China, probably because as a non-pathogenic species it is likely to be considered unimportant, and because of its similarity to Anguillicola globiceps). It is likely that it is present in other countries in this region and it has been reported from Thailand (Moravec, 2006) but there have been very few or no published reports of eel parasites from many parts of Eastern Asia. Its natural range probably coincides with that of its preferred host Anguilla japonica.

Factors limiting distribution
 
Although A. crassus is potentially able to infect Atlantic eels throughout their entire range and has a wide tolerance of environmental conditions, it also exhibits a preference for some physico-chemical conditions, notably of temperature and salinity.
 
Temperature
Although present in the Baltic Sea, A. crassus was slow to colonise the Nordic countries of Norway and Sweden, and Finland is still believed to be free of infection. When it was first reported from Sweden, it was from coastal areas where water temperatures were raised by thermal effluents from power stations (Hoglund et al, 1992). Only much later was it reported from inland waters (Hoglund and Thomas, 1992).
 
The temperature tolerance of A. crassus was investigated experimentally by Knopf et al. (1998) who infected Anguilla anguilla and maintained them over a range of temperatures for 4 months. They found that larval development was significantly retarded at low temperatures. Larval L3 could survive 4 months at 4° C, but were unable to invade the swimbladder wall. Adults exhibited decreased growth and reproduction rates and increased mortality compared to those kept at 18° C. These data thus support the conclusions drawn from field studies that the spread of the parasite in boreal regions may be restricted by temperature.
 
Salinity
Field data have indicated that although A. crassus is primarily a freshwater species, it can nevertheless tolerate enhanced salinity levels. Køie (1988, 1991) found that whilst the parasite could survive enhanced salinity in the Baltic sea, it was normally absent from sea water eel farms. Reimer et al. (1994) also noted that the distribution of A. crassus in the Baltic sea indicated that it was tolerant of, and able to be transmitted under, conditions of enhanced salinity. The parasite has also been reported to be able to survive in eels in the tidal reaches of the River Thames (Pilcher and Moore, 1993) and in Italian coastal lagoons with slightly enhanced salinity, although not in the most saline ones (Kennedy et al., 1997; Di Cave et al., 2001).
 
In experimental laboratory studies Kennedy and Fitch (1990) showed that the proportion of eggs hatching decreased with increasing salinity such that only 6% hatched in 100% seawater. The survival of L2s also declined with increasing salinity but even though 50% survived 10 days in 100% seawater, larval infectivity declined and none survived longer than 15 days. Similar findings were reported by De Charleroy et al. (1990).
 
Kennedy and Fitch (1990) also reported that there was no loss of viability of adults or L4s or eggs of A. crassus in Anguilla anguilla maintained in full sea water for up to 4 weeks. More detailed studies on survival of A. crassus in saline conditions were undertaken by Scholz and Zerbst-Boroffka (1994), who found that its body fluids were isosmotic with those of the eel host (Anguilla anguilla), but differed in ionic composition, and by Kirk et al. (2000a, b; 2002). These authors found that adult parasites tolerated seawater by osmoconformation with the blood plasma of their eel hosts. The majority of parasites (90%) osmoconformed with hosts after 2 weeks in sea water following acute transfer and survived for a long period, up to and exceeding 3 months. A small proportion of pre-adults and adult parasites were unable to withstand the osmotic stress and died, but the reasons for this are not known. These same authors concluded that whilst A. crassus was unable to be transmitted to eels in seawater, due to the absence of suitable copepod hosts, it could be transmitted in estuaries using species such as Eurytemora affinis and it could survive the transition to sea water in eels already infected in freshwater, and continue to survive and reproduce in them for up to 6 months. It was thus possible for the parasite to be disseminated naturally by eel movements in coastal waters.

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

Asia

ChinaPresentPresent based on regional distribution.
-FujianPresentNativeNagasawa et al., 1994In culture
-HubeiPresentNativeNagasawa et al., 1994In culture
JapanPresentPresent based on regional distribution.
-HokkaidoWidespreadNativeNagasawa et al., 1994Especially in culture
-HonshuWidespreadNativeNagasawa et al., 1994Culture in wild
Korea, Republic ofPresentNativeKim et al., 1989Reported from culture
TaiwanWidespreadNativeMünderle et al., 2006Wild and in culture
ThailandPresentMoravec, 2006
TurkeyPresentIntroduced Invasive Genç et al., 2005In several rivers

Africa

EgyptPresentIntroduced Invasive Mohamed and Nouh, 2004
MoroccoLocalisedIntroduced Invasive Loukilli and Belghyti, 2007Known since 1999
RéunionLocalisedIntroduced Invasive Sasal et al., 2008Reported from African eel species, and believed to have been introduced by man
TunisiaLocalisedIntroduced Invasive Maamouri et al., 1999In one lake system, but extending range

North America

CanadaPresentPresent based on regional distribution.
-New BrunswickWidespreadIntroduced Invasive Aieta and Oliveira, 2009
-Newfoundland and LabradorWidespreadIntroduced Invasive Aieta and Oliveira, 2009
-Nova ScotiaWidespreadIntroduced Invasive Aieta and Oliveira, 2009
-Prince Edward IslandWidespreadIntroduced Invasive Aieta and Oliveira, 2009
USAPresentPresent based on regional distribution.
-MaineWidespreadIntroduced Invasive Aieta and Oliveira, 2009
-MarylandWidespreadIntroduced Invasive Barse et al., 2001
-MassachusettsWidespreadIntroduced Invasive Aieta and Oliveira, 2009
-New YorkLocalisedIntroduced Invasive Machut and Limburg, 2007In Hudson River watershed
-North CarolinaPresentIntroduced Invasive Moser et al., 2001
-Rhode IslandPresentIntroduced Invasive Aieta and Oliveira, 2009
-South CarolinaLocalisedIntroduced Invasive Fries et al., 1996
-TexasPresentIntroducedcirca 1995 Invasive Johnson et al., 1995First record in N. America

Europe

AustriaLocalisedIntroduced Invasive Schabuss et al., 2005Foci in stocked lakes
BelarusPresentIntroduced Invasive Moravec, 2006
BelgiumWidespreadIntroduced Invasive Schabuss et al., 1997First records 1980s
Czech RepublicWidespreadIntroduced Invasive Baruš et al., 1999aIntroduced with eel stocking
DenmarkWidespreadIntroduced Invasive Køie, 1991Introduced with eel stocking
EstoniaPresentIntroduced Invasive Höglund and Thomas, 1992
FranceWidespreadIntroduced Invasive Dupont and Petter, 1988Early introduction into south
GermanyWidespreadIntroduced Invasive Sures et al., 1999a; Neumann, 1985; Hartmann, 1987; Würtz et al., 1998First record from Europe in Weser-Ems in 1982. Now in all major rivers.
GreeceLocalisedIntroduced Invasive Moravec, 2006
HungaryLocalisedIntroduced Invasive Molnár, 1994Usually in stocked lakes, especially Lake Balaton
IrelandWidespreadIntroduced Invasive Evans and Matthews, 1999; Evans et al., 2001First report 1998, but now spreading rapidly. Introduced with eel trade
ItalyWidespreadIntroduced Invasive Canestri-Trotti, 1987; Koops and Hartmann, 1989Introduced with eels imported from France. Mainly in eel culture
MacedoniaPresentMoravec, 2006
NetherlandsWidespreadIntroduced Invasive Borgsteede et al., 1999First reported soon after arrival in Europe
NorwayLocalisedIntroduced Invasive Mellergaard, 1988Slower colonisation near limit of the species range
PolandWidespreadIntroduced Invasive Rolbiecki, 2008
PortugalWidespreadIntroduced Invasive Maíllo et al., 2005Often in coastal lagoons
Russian FederationPresentPresent based on regional distribution.
-Central RussiaLocalisedIntroduced Invasive Rodjuk and Shelenkova, 2006Mainly around Kaliningrad and Baltic Sea
SlovakiaLocalisedIntroduced Invasive Moravec, 2006In River Danube system
SpainLocalisedIntroduced Invasive Aguilar et al., 2005Localisation may reflect areas of study
SwedenLocalisedIntroduced Invasive Hellstrom et al., 1988; Höglund and Thomas, 1992Initially only in thermal effluents but now spreading more widely in south.
UKWidespreadIntroduced Invasive Kennedy and Fitch, 1990; Lyndon and Pieters, 2005Introduced with eel trade in south and east in 1987. Now widespread all over including Scotland.

History of Introduction and Spread

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A. crassus is the most efficient invasive helminth known (Nagasawa et al., 1994) but its rapid spread throughout the distribution range of the two species of Atlantic eel has been facilitated by, and is due in no small measure to, the uncontrolled inter-continental transfer of live eels. Its spread has, in fact, been so rapid that it has exceeded the rate at which it can be documented and any published account is invariably out of date. References cited in the table therefore tend to report the early stages of invasion as it is not possible to keep pace with the parasite’s subsequent spread throughout a country. It is already widespread throughout Europe (Ashworth and Blanc, 1997; Kirk, 2003; Moravec, 1992, 2006) and it can be predicted that its distribution range in Atlantic eels will become congruent with that of the eels themselves.

The first record of A. crassus outside the region of East Asia came from eels in the Weser-Ems system in North Germany in 1982 (Neumann, 1985). It is now almost certain that it arrived with a load of live eels imported into Bremerhaven from Taiwan (Koops and Hartmann, 1989). Thereafter the parasite spread rapidly, being recorded from the Ruhr Lake, Weser and Elbe estuary in 1986 (Moravec and Taraschewski, 1988) and subsequently spread to Berlin and the Rhine (Peters and Hartmann, 1986). In each locality its numbers increased rapidly after introduction: in the Elbe, for example, it was absent from eels in 1985, but by 1986 between 6 and 27% of eels were infected (Möller et al, 1991). As a consequence of further imports of live eels from East Asia as well as transfers of eels from different countries within Europe, A. crassus spread throughout the continent. On genetic grounds, Wielgoss et al. (2008) suggest that the path of colonisation has been from country to country from a localised source. There is no doubt at all that the rapidity of this spread was in large measure assisted by the uncontrolled inter- and intra-continental transfer of live eels. The re-stocking of lakes and rivers with eels, officially and unofficially, as well as providing eels for aquaculture ponds, promoted wide dispersal. In England, the first introduction of A. crassus was detected in 1987. By 1988 it was evident that it was dispersing from two foci in the east of the country, London and East Anglia, which were also the two main centres for the import of live eels (Kennedy and Fitch, 1990). Movements of eels around any country for re-stocking can disseminate the parasite even further (Belpaire et al., 1989; Koops and Hartmann, 1989).
 
The extraordinary rate at which A. crassus can spread throughout a continent is exemplified particularly well in North America. The first record of the species in the American continent came from an unidentified eel in an aquaculture facility in Texas (Johnson et al., 1995; Fries et al., 1996) and this again appears to be directly related to the importation of eels into the country. It has subsequently been found in wild populations of the American eel Anguilla rostrata and is still spreading rapidly northwards throughout the range of this host along the North Atlantic coast into Canada, having now reached as far as Cape Breton (Barse and Secor, 1999; Barse et al., 2001; Machut and Limberg, 2007; Aieta and Oliveira 2009; Rockwell et al., 2009). Thus, in only 13 years it has spread throughout the eastern seaboard, i.e. virtually the whole range of Anguilla rostrata. It is believed on genetic grounds that the parasite was imported directly into the USA from Japan (Wielgoss et al., 2008) rather than from Europe.
 
Recently A. crassus has been reported from species of African eels on Réunion Island in the Pacific Ocean. It is believed that it was introduced there in the course of eel imports rather than by natural movements of infected eels (Sasal et al. 2008).

Introductions

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Introduced toIntroduced fromYearReasonIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
Germany circa 1982 Aquaculture (pathway cause) Yes Koops and Hartmann (1989); Neumann (1985) First introduction in Europe, to Bremerhaven probably from Taiwan, imported with live eels
Italy France Aquaculture (pathway cause) Introduced with eel imports
Texas Asia   Aquaculture (pathway cause) Yes Wielgoss et al. (2008) From Asia, probably Japan, to Texas, N. America
UK 1987 Aquaculture (pathway cause) Introduced with eel imports

Risk of Introduction

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Although movements of eels for purposes of stocking and farming have played a major role in the rapid and widespread dissemination of A. crassus (Kennedy and Fitch, 1990; Belpaire et al., 1989) it is important to appreciate that A. crassus itself possesses many of the attributes of a successful coloniser (Kennedy and Fitch, 1990). These include: 1) a high reproductive potential, 2) a relatively simple life cycle with a low degree of specificity towards its intermediate host, including estuarine species of copepod, 3) the ability to use a wide range of fish species as paratenic hosts, 4) free living L2 larvae capable of surviving and remaining infective for long periods in freshwater of a range of salinities and in sea water, 5) the capability of infecting eels of all sizes, 6) the ability to survive for long periods in eels living in sea water, and 7) escaping the restrictions of a narrow specificity to its definitive host by using a species of fish that is itself widespread in distribution and capable of surviving a wide range of habitat and environmental conditions. It also occupies the swimbladder of an eel, a habitat in which there is no competitor. Every eel within the temperature and pH range of A. crassus is thus potentially at risk of infection. A combination of the colonisation abilities of the parasite, the natural movements of eels themselves and transfers of eels by man have enabled A. crassus to colonise Europe, North America and North Africa within 25 years: this is an extraordinary achievement.

Pathogen Characteristics

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A. crassus is, like all anguillicolids, parasitic as an adult in the lumen of the swimbladder of its eel host. Eels acquire infections by ingestion of an infected copepod, the intermediate host, or by ingestion of an infected fish, a paratenic host. In either case, the L3 larvae migrate to the swimbladder wall of the eel, where they moult to the L4 stage and eventually move into the lumen of the swimbladder and develop into adults. The adult is a large nematode with a stout body tapering at each end. It is a blood feeder with a well-developed buccal capsule, a row of circumoral teeth and a muscular oesophagus. The presence of blood and the breakdown products of blood in the intestine give the whole nematode a dark, almost black, appearance. The sexes are separate. The body wall and other organs are typical of nematodes in general. Males range in length from about 6-23 mm and in width from 0.3 to 1.8 mm, whilst females range from 13-45 mm in length and from 1.2 – 5.0 mm in width. Females in particular appear very robust. They are ovoviviparous: the uterus occupies most of the space of the body and contains eggs which in turn contain developing embryos and fully formed larvae (L2). A single female may contain up to 500,000 eggs (Kennedy and Fitch, 1990). The eggs may hatch inside the female to release the larvae, or may be shed from the female and hatch in the pneumatic duct so that the larvae pass out to the exterior with the eel faeces. Females die in the swim bladder, which then contains live worms of each sex as well as disintegrating parasite tissues and numerous eggs. The presence of adult parasites, both living and dead, brings about characteristic changes in the thickness of the swimbladder wall and affects the gas content and functioning of the swimbladder.

A. crassus can be distinguished from Anguillicola globiceps by the characteristic oesophagus of this latter species, which is conspicuously inflated at its anterior end, and from other species of Anguillicoloides by that fact that its cephalic end is not expanded and it lacks a distinct neck constriction (Moravec, 2006).

Hosts/Species Affected

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The only species deleteriously affected by A. crassus are the Atlantic eels, Anguilla anguilla and Anguilla rostrata. The parasite is harmless to Anguilla japonica and other species of Pacific eel. It appears that the parasite and Anguilla japonica may have co-evolved together such that this eel has acquired a measure of resistance to A. crassus (Egusa, 1979; Kim et al., 1989; Knopf and Lucius, 2008).

As far as is known, all individuals of Anguilla anguilla are equally at risk of infection by A. crassus: small individuals by eating infected copepods and large individuals by eating infected fish. There is no resistance to re-infection (Haenen et al., 1996) and antibodies produced against the parasite have no protective function (Knopf and Lucius, 2008). Once A. crassus has entered a lake or eel farm, its prevalence often rises to 100%, and transmission rates and infection levels may be very high when eel densities are themselves high as in eel farms or shallow lakes (Molnár et al., 1994; Baruš et al. 1999a). Stress in individual eel hosts may predispose them to disease (Gollock et al., 2005a).

Host Animals

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Biology and Ecology

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Genetics

The genetics of this species have been intensively studied, for more details see Heitlinger et al. (2009).

 

Climate

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ClimateStatusDescriptionRemark
C - Temperate/Mesothermal climate Preferred Average temp. of coldest month > 0°C and < 18°C, mean warmest month > 10°C
Cf - Warm temperate climate, wet all year Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year
Cs - Warm temperate climate with dry summer Tolerated Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers
Cw - Warm temperate climate with dry winter Tolerated Warm temperate climate with dry winter (Warm average temp. > 10°C, Cold average temp. > 0°C, dry winters)
D - Continental/Microthermal climate Tolerated Continental/Microthermal climate (Average temp. of coldest month < 0°C, mean warmest month > 10°C)

Notes on Natural Enemies

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There are no known natural enemies of A. crassus as such. There will always be some mortality of L2s through being eaten by copepods that are not suitable intermediate hosts and of L3s in paratenic hosts being eaten by fish other than eels or by birds, but there is no known predator or hyperparasite of adult parasites.

Pathway Causes

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CauseNotesLong DistanceLocalReferences
Aquaculture Yes Yes Fries et al., 1996; Kennedy and Fitch, 1990
Interbasin transfersTransfers of eels by man Yes Yes
Interconnected waterwaysNatural movements of eels Yes Yes

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Aquaculture stockTransfers of eels by air and by road. As many transfers are illegal, details are often unavailable. Yes Yes Kennedy and Fitch, 1990

Impact Summary

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CategoryImpact
Fisheries / aquaculture Negative
Native fauna Negative
Other Negative

Economic Impact

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Despite many reports and references to the damage caused by A. crassus to Anguilla anguilla in eel farms in the Far East, especially in Japan, and to eels in Europe, there is little or no information actually published to quantify the damage in economic terms. Køie (1991), for example, refers to mortalities of 15-65% in a Dutch eel farm and increased mortalities from 10-20 % in other eel farms, but without placing any economic value on these losses.

In the cases of the eel mortalities attributed to A. crassus in European lakes, the only figures available relate to mortalities. Thus, Molnár et al. (1991, 1994) state that in 1991, 200 tonnes of eels died in Lake Balaton, and in 1992 40 tonnes. Baruš et al. (1999a) similarly quote a figure 3.5 tonnes of eels killed in the Vranov Dam in 1994, but no financial values have been attached to these losses. It must be presumed that there was a severe economic loss to professional eel fishermen as a consequence of the mortalities but no figures are available to support this presumption.
 
More recently, Taraschewski (2006) has made the point that as eel farming declines throughout Europe, even in Italy, in response to increasing energy and labour costs and as the price of ever scarcer elvers increases, A. crassus no longer poses so much of a threat and so will have a greatly reduced economic impact.

Environmental Impact

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Impact on biodiversity

The effects of A. crassus on wild eel populations are more difficult to study than those on captive ones, but experiments suggest that infected eels are more likely to die in adverse conditions (Didziulis, 2006). Mass mortalities have been reported among wild eels, but only when there have been particular combinations of unfavourable circumstances (for more details, see datasheet on Anguillicolosis). Concern has been expressed that severe damage to the swimbladder may reduce the ability of eels to migrate to their spawning grounds in the Sargasso Sea, which could have a severe impact on the future of the population (Didziulis, 2006). Such a decline could have significant effects on ecosystem community structure.

Threatened Species

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Threatened SpeciesConservation StatusWhere ThreatenedMechanismReferencesNotes
Anguilla anguilla (European eel)CR (IUCN red list: Critically endangered) CR (IUCN red list: Critically endangered)Parasitism (incl. parasitoid); PathogenicPalstra et al., 2007; Sjöberg et al., 2009

Risk and Impact Factors

Top of page Invasiveness
  • Proved invasive outside its native range
  • Has a broad native range
  • Abundant in its native range
  • Highly adaptable to different environments
  • Fast growing
  • Has high reproductive potential
  • Has propagules that can remain viable for more than one year
Impact outcomes
  • Host damage
  • Negatively impacts aquaculture/fisheries
Impact mechanisms
  • Parasitism (incl. parasitoid)
  • Pathogenic
Likelihood of entry/control
  • Highly likely to be transported internationally accidentally
  • Highly likely to be transported internationally illegally
  • Difficult to identify/detect as a commodity contaminant
  • Difficult to identify/detect in the field
  • Difficult/costly to control

References

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Aguilar A; Âlvarez MF; Leiro JM; Sanmartín ML, 2005. Parasite populations of the European eel (Anguilla anguilla L.) in the Rivers Ulla and Tea (Galicia, northwest Spain). Aquaculture, 249(1/4):85-94. http://www.sciencedirect.com/science/journal/00448486

Aieta AE; Oliveira K, 2009. Distribution, prevalence, and intensity of the swim bladder parasite Anguillicola crassus in New England and eastern Canada. Diseases of Aquatic Organisms, 84(3):229-235. http://www.int-res.com/abstracts/dao/v84/n3/p229-235/

Ashworth ST, 1994. Possible regulation in the Anguillicola crassus host-parasite system. In: Parasitic diseases of fish [ed. by Pike, A. W.\Lewis, J. W.]. Tresaith, Dyfed, UK: Samara Publishing, 141-150.

Ashworth ST; Blanc G, 1997. Anguillicola crassus, an aggressive coloniser recently introduced into European eel stocks. (Anguillicola crassus, un colonisateur agressif recemment introduit dans les stocks europeeans d'anguilles.) Bulletin Francais de Peche et Pisciculture, 1997:345-352.

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Organizations

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Denmark: North European and Baltic Network on Invasive Alien Species (NOBANIS), Web-based service, nobanis@sns.dk, http://www.nobanis.org/

Contributors

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04/10/09 Original text by:

Clive Kennedy, University of Exeter, School of Biosciences, Geoffrey Pope Building, Stocker Road, Exeter, EX4 4QD, UK

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