Anguilla anguilla

Geographic Range

The geographic range of adult European eels includes the English Channel and coasts of the Mediterranean Sea and northern Atlantic Ocean from Iceland to Mauritania (Ringuet et al., 2002). Their range also encompasses the Baltic and North Seas, as well as all accessible continental or coastal hydrosystems (Ringuet et al., 2002). In the early spring months, European eels migrate to the Sargasso sea for breeding. Larvae are hatched from the Sargasso Sea and can also be found along the coast of Europe. Silver (juvenile) stage eels of Anguilla anguilla live in tributaries along the European coast.

• Biogeographic Regions
• palearctic palearctic
  • native native
• atlantic ocean atlantic ocean
  • native native
• mediterranean sea
  • native native

Habitat

Depending on the lifestage of the individual eel, European eels can be found in marine, freshwater, and brackish aquatic environments. Typically, the European eel is found in depths of 0-700 m, most often on the floor of the ocean or river in which it is living.

• Habitat Regions
• saltwater or marine saltwater or marine
• freshwater freshwater

• Aquatic Biomes
• benthic benthic
• coastal coastal
• brackish water brackish water

• Other Habitat Features
• estuarine estuarine

Physical Description

The appearance of European eels varies greatly depending on life stage. As leptocephali, European eels are small, leaflike, and transparent (Deelder, 1970). After metamorphosing into the silver stage, European eels appear silvery in color with elongated dorsal and anal fins that are continuous with the caudal fin (Deelder, 1970). European eels lack pelvic fins (Deelder, 1970). Upon full sexual maturation, European eels develop enlarged eyes, lose their ability to feed, and turn green, yellow or brownish in color (Van Ginniken and Thillhart, 2000).

Female eels are generally substantially larger than males. The largest recorded mass of a female eel is 6.599 g (Dekker, van Os and van Willigen, 1998). The maximum published length of a European eel was 133 cm.

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger

Development

European eels begin their life cycle as eggs on the bottom of the Sargasso Sea. They hatch as leptocephali, leaf-like larvae (Tsukamoto, Nakai and Tesch, 1998). After hatching, larvae spend a maximum of one year migrating to Europe, or occasionally North America, via ocean currents. The larvae will then metamorphose into 'glass eels,' the next stage of the life cycle, and enter estuarine areas. Male glass eels contineu to grow for approximately 6 to 12 years; females for 9 to 20 years (Deelder, 1970). After a final metamorphosis, European eels migrate back to the Sargasso Sea to spawn.

• Development - Life Cycle
• metamorphosis metamorphosis

Reproduction

Upon reaching sexual maturity, European eels migrate from freshwater streams back to the Sargasso Sea in order to spawn and die in the late winter months to the early summer months. European eel males release sperm into the water in which female European eels have already laid eggs, thereby fertilizing the eggs (Horie et al., 2004). Very little is known about the actual spawning mechanism, and time to hatching is variable.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

European eels spawn during the late winter to early spring months. There is little information on their reproduction, but since European eels are closely related to Japanese eels, Anguilla japonica , similar breeding patterns might be assumed. Female A. japonica can lay from 2,000,000 to 10,000,000 eggs, but die soon after spawning (Deelder, 1970). Eel larvae are independent from time of birth until time of death.

• Key Reproductive Features
• semelparous semelparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • external external
• broadcast (group) spawning
• oviparous oviparous

European eels invest a substantial amount of energy in reproduction, and die shortly thereafter (Deelder, 1970). Consequently, the only resource that female eels give to their offspring is enough food source to last the egg until hatching. After hatching, the larvae are completely independent and able to find food (Lecomte-Finiger, 1994).

• Parental Investment
• no parental involvement
• pre-fertilization
  • provisioning

Lifespan/Longevity

The lifespan of European eels is dependent on maturation time because once eels mature and spawn, they die. European eels can spawn as early as 7 years old. The maximum reported age of a European eel in the wild is 85 years (Dekker, van Os and van Willigen, 1998).

Behavior

European eels are essentially a solitary species. Although numerous eels can be found in a single location, there is no evidence that any form of schooling is present (Suzuki et al, 2003). European eels migrate to various regions during different stages of their life. They transport themselves by actively swimming with ocean currents (Deelder, 1970). European eels are active mainly during the day.

• Key Behaviors
• natatorial natatorial
• diurnal diurnal
• motile motile
• migratory migratory
• solitary solitary

Communication and Perception

European eels sense the environment using their sense of taste. They have been shown to locate necessary amino acids via chemotaxis (Sola and Tongiorgi, 1998). European eels also utilize olfaction, most probably for homing purposes. There is little if any documentation of social communication between eels (Deelder, 1970).

• Perception Channels
• visual visual
• tactile tactile
• chemical chemical

Food Habits

European eels have completely different diets during different life stages. No food contents have ever been discovered in the guts of leptocephali, therefore their diet is unknown (Fisheries Global Information System, 2005). Glass eels consume insect larvae, dead fish, and small crustaceans (Sinha and Jones, 1975). Adult eels have a fairly broad diet and eat freshwater, marine, or terrestrial fauna. Their primary food source is aquatic invertebrates, but they will eat essentially any food they can find-- even dead organisms (Sinha and Jones, 1975). European eels are reported to leap out of the water during the winter and feed on terrestrial invertebrates (Deedler, 1970).

• Primary Diet
• carnivore carnivore
  • insectivore insectivore
  • eats non-insect arthropods
  • molluscivore molluscivore
  • eats other marine invertebrates
  • scavenger scavenger

• Animal Foods
• fish
• eggs
• carrion carrion
• insects
• mollusks
• terrestrial worms
• aquatic or marine worms
• aquatic crustaceans
• zooplankton zooplankton

• Other Foods
• detritus detritus

Predation

European eels are preyed upon by larger eels and other fish and fish-consuming birds, such as cormorants ( Phalacrocorax ) and herons ( Ardeidae ) (Deelder, 1970). One defense mechanism employed by eels is that they hide under rocks and burrow in the sand, thus avoiding their predators. The coloring of eels at various life stagies (i.e. the transparency of leptocephali, the dark grey to green color of adults, etc.) also serves as camouflage.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

European eels are both a food source and a predator of organisms in their ecosystem. They are consumed by birds and large predatory fish (Deelder, 1970). European eels also act as a host for the nematode Aguillicola crassus which infects the swim bladders of European eels (Deelder, 1970). European eels distribute nutrients between marine and freshwater ecosystems because they migrate between those habitats (Deelder, 1970).

Economic Importance for Humans: Positive

European eels are a popular food source for humans, especially in Europe and Asia. The eels also feed on the eggs of predatory fish such as trout, which keep ecosystems from overpopulation (Deelder, 1970).

• Positive Impacts
• food food
• controls pest population

Economic Importance for Humans: Negative

European eels thrive on a diet of marine and freshwater fauna, so impact populations of other marine and freshwater organisms (Deelder, 1970). There are no direct adverse effects to humans.

Conservation Status

European eel populations are not currently threatened.

Other Comments

European eels can survive, and even reproduce, at temperatures as low as 0°C. Optimum temperatures for gametogenesis in Anguilla anguilla are between 0°C and 30°C (Deelder, 1970)-- quite a large range!

Additional Links

Encyclopedia of Life

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Melissa Skupin (author), University of Michigan-Ann Arbor, Kevin Wehrly (editor, instructor), University of Michigan-Ann Arbor.

References

Deelder, C. 1970. Synopsis of biological data of the eel Anguilla anguilla (Linnaeus, 1758). FAO Fish. Synop. , 80: 68.

Dekker, W., B. van Os, J. van Willigen. 1998. Minimal and maximal size of eel.. L'ANGUILLE EUROPENNE. 10E REUNION DU GROUPE DE TRAVAIL "ANGUILLE" EIFAC/ICES..

Lecomte-Finiger, R. 1994. The Early Life of the European Eel. Nature , 370: 424-425.

Okamura, A., H. Zhang, T. Utoh, A. Akazawa, Y. Yamada, N. Horie, N. Mikawa, S. Tanaka, H. Oka. 2004. Artificial hybrid between Anguilla anguilla and A. japonica. Journal of Fish Biology , 64/5: 1450.

Ringuet, S., F. Muto, C. Raymakers. 2002. Eels: Their Harvest and Trade in Europe and Asia. Traffic Bulletin , 19/2: 2-27.

Sinha, V., J. Jones. 1975. The European Freshwater Eel . Liverpool: Liverpool University Press.

Sola, C., P. Tongiorgi. 1998. Behavioural responses of glass eels of Anguilla anguilla to non-protein amino acids. Journal of Fish Biology , 53/6: 1253.

Tsukamoto, K., I. Nakai, W. Tesch. 1998. Do all freshwater eels migrate?. Nature , 396: 635-636.

Tsukamoto, K., T. Otake, N. Mochioka, T. Lee, H. Fricke, T. Inagaki, J. Aoyama, S. Ishikawa, M. Miller, S. Kimura, H. Hasumoto, M. Oya, Y. Suzuki. 2003. Seamounts, new moon and eel spawning: The search for the spawning site of the Japanese eel. Environmental Biology of Fishes , 66: 221-229.

Van Ginneken, V., G. Van Den Thillart. 2000. Physiology: Eel fat stores are enough to reach the Sargasso. Nature , 403: 156-157.

2001. "Fisheries Global Information System" (On-line). Accessed December 01, 2005 at http://www.fao.org/figis/servlet/species?fid=2203 .