Anguillicola crassus
Encyclopedia
Anguillicoloides crassus is a parasitic
nematode
worm that lives in the swimbladders
of eels
(Anguilla
spp.) and appears to spread easily among eel populations after introduction to a body of water. It is considered to be one of the threats to the sustainability of populations of European eel
(Anguilla anguilla). It was introduced to the European continent in the 1980s, where it was reported independently from Germany and Italy in 1982, having probably been introduced from Taiwan. It is thought to have reached England in 1987 from continental Europe. It is a natural parasite of the Japanese eel
in its native range.
The life cycle of Anguillicoloides crassus begins when the adult nematode releases thousands of eggs in the eel's swimbladder. The eggs pass through the eel's digestive tract and the larvae emerge in the water and settle onto the substrate. They are ingested by their intermediate host, which is often a copepod
or other crustacean
but may also be a fish. The nematode larva reaches its infective stage within this intermediate host. The host is eaten by an eel, and the nematode finds its way from the eel's digestive tract to its swimbladder. An eel with an advanced parasite load shows symptoms such as bleeding lesions and swimbladder collapse. The eel becomes more susceptible to disease, its rate of growth slows, and if the infestation is severe enough, it may die. Since the swimbladder is the buoyant
organ which allows the eel to swim, a severe parasite infestation can hamper its ability to reach its spawning
grounds.
The state of being colonized by Anguillicola nematodes is termed anguillicolosis.
Parasitism
Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Traditionally parasite referred to organisms with lifestages that needed more than one host . These are now called macroparasites...
nematode
Nematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...
worm that lives in the swimbladders
Gas bladder
The swim bladder, gas bladder, fish maw or air bladder is an internal gas-filled organ that contributes to the ability of a fish to control its buoyancy, and thus to stay at the current water depth without having to waste energy in swimming...
of eels
Anguillidae
Anguillidae is a family of fishes that contains the freshwater eels. There are 19 species/subspecies in this family, all in genus Anguilla. They are catadromous, meaning they spend their lives in freshwater rivers, lakes, or estuaries and return to the ocean to spawn...
(Anguilla
Anguilla
Anguilla is a British overseas territory and overseas territory of the European Union in the Caribbean. It is one of the most northerly of the Leeward Islands in the Lesser Antilles, lying east of Puerto Rico and the Virgin Islands and directly north of Saint Martin...
spp.) and appears to spread easily among eel populations after introduction to a body of water. It is considered to be one of the threats to the sustainability of populations of European eel
European eel
The European eel, Anguilla anguilla, is a species of eel, a snake-like, catadromous fish. They can reach in exceptional cases a length of 1½ m, but are normally much smaller, about 60–80 cm, and rarely more than 1 m....
(Anguilla anguilla). It was introduced to the European continent in the 1980s, where it was reported independently from Germany and Italy in 1982, having probably been introduced from Taiwan. It is thought to have reached England in 1987 from continental Europe. It is a natural parasite of the Japanese eel
Japanese eel
The Japanese eel, Anguilla japonica, is a species of eel found in Japan, Korea, Vietnam the East China Sea and the northern Philippines. Like the all the eels of its family, it is catadromous, meaning it lives parts of its life in both freshwater and saltwater. The specific spawning grounds have...
in its native range.
The life cycle of Anguillicoloides crassus begins when the adult nematode releases thousands of eggs in the eel's swimbladder. The eggs pass through the eel's digestive tract and the larvae emerge in the water and settle onto the substrate. They are ingested by their intermediate host, which is often a copepod
Copepod
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...
or other crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
but may also be a fish. The nematode larva reaches its infective stage within this intermediate host. The host is eaten by an eel, and the nematode finds its way from the eel's digestive tract to its swimbladder. An eel with an advanced parasite load shows symptoms such as bleeding lesions and swimbladder collapse. The eel becomes more susceptible to disease, its rate of growth slows, and if the infestation is severe enough, it may die. Since the swimbladder is the buoyant
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
organ which allows the eel to swim, a severe parasite infestation can hamper its ability to reach its spawning
Spawn (biology)
Spawn refers to the eggs and sperm released or deposited, usually into water, by aquatic animals. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning...
grounds.
The state of being colonized by Anguillicola nematodes is termed anguillicolosis.
Further reading
- 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 IchthyologyJournal of Applied IchthyologyThe Journal of Applied Ichthyology is a scientific journal on ichthyology, marine biology and oceanography, the continuation of several differently-named journals on these subjects...
, 1: 41–45.
External links
- A. crassus as a parasite of eel swimbladders (pdf)
- "Anguillicola crassus (Kuwahara, Niimi and Hagaki, 1974)" at Internet ArchiveInternet ArchiveThe Internet Archive is a non-profit digital library with the stated mission of "universal access to all knowledge". It offers permanent storage and access to collections of digitized materials, including websites, music, moving images, and nearly 3 million public domain books. The Internet Archive...
- JNCC website