Anarrhichthys ocellatusDoctorfish(Also: northern wolffish)

Geographic Range

Wolf-eels are found in the temperate North Pacific in coastal waters from the Sea of Okhotsk and the Sea of Japan to the Aleutian islands and along the western coast of North America to Baja California. (Feeney, et al., 2007; Froese, 2008)

Habitat

Wolf-eels are exclusively marine, found in shallow, cold, coastal waters. They have been found in depths as low as 226 meters, but are generally found in shallow water. They are demersal in their habits, being found almost exclusively in sheltered, rocky, sub-tidal areas or near rocky structures in areas with sandy bottoms. They remain in a rock shelter unless excluded by a larger wolf-eel or octopus. Juvenile stages are pelagic for their first 2 years of life. (Froese, 2008; Sempier, 2003)

  • Range depth
    0 to 226 m
    0.00 to 741.47 ft

Physical Description

Wolf-eels are large, eel-like fish similar in appearance to morays (Muraenidae). They are up to 240 cm in total length and a maximum of 18.4 kg. They have robust heads and large pectoral fins with 18 to 24 rays. The body is long and tubular, tapering to a pointed tail. Wolf-eels have the most elongated morphology of other wolf-fishes (Anarhichadidae), which are mostly only moderately elongate. They have a single, long dorsal fin that stretches the length of their body, tapering to a point at the tail. It has 218 to 250 flexible spines. The anal fin is also long, with 180 to 233 soft rays. There are no pelvic fins. Wolf-eels have a single pair of nostrils, a moderately well-developed lateral line, and no swim bladder. These fish have very robust, caniniform teeth. (Froese, 2008)

  • Range mass
    18.4 (high) kg
    40.53 (high) lb
  • Range length
    240 (high) cm
    94.49 (high) in

Development

Wolf-eel eggs are protected by both parents until they hatch at 91 to 112 days. Juveniles are pelagic, drifting in water currents until they reach 2 years old, at which point they settle in shallow, coastal areas with structures that provide denning sites. (Froese, 2008; Sempier, 2003)

Reproduction

Males and females form monogamous pairs at about 4 years old, or 91.4 cm in length. Some evidence suggests they mate for life. (Sempier, 2003)

Estimates of age at sexual maturity vary in the literature, some sources suggest that males and females for mated pairs at about 4 years old, or 91.4 cm in length, other sources suggest female maturity is reached at 7 years old. Females can lay up to 10,000 eggs at a time. Eggs take 91 to 112 days to hatch. Fertilization is external, but few details about mating behavior or periodicity are reported. (Sempier, 2003)

  • Breeding interval
    Breeding interval is not reported.
  • Breeding season
    Wolf-eels spawn from October through the winter.
  • Range number of offspring
    10,000 (high)
  • Range time to hatching
    91 to 112 days
  • Range age at sexual or reproductive maturity (female)
    7 (high) years
  • Average age at sexual or reproductive maturity (female)
    4 years
  • Average age at sexual or reproductive maturity (male)
    4 years

Both males and females will wrap their bodies around their egg masses to protect them until hatching. They aggressively defend egg masses in their rocky dens until they hatch. (Froese, 2008)

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • protecting
      • male
      • female

Lifespan/Longevity

Wolf-eel maximum lifespan is not reported. Age at maturity occurs at 4 to 7 years, suggesting these may be long-lived fish. (Froese, 2008; Sempier, 2003)

Behavior

Wolf-eels remain in their rock crevices during the day and emerge to forage at night. They roam widely looking for fish and invertebrate prey, but have a great deal of site fidelity - returning to the daytime dens and inhabiting them for long periods of time. Vacated dens are rapidly inhabited by other wolf-eels, though, so they may patrol potential den sites regularly. They seem to be territorial, aggressively defending their den area. Wolf-eels are occasionally caught by hook and line anglers, so there may be some limited daytime activity. (Hulberg and Graber, 1980)

Home Range

Home range sizes are not reported for wolf-eels

Communication and Perception

There is little information available on communication and perception in wolf-eels. It is likely that the most important modes of perception are vision and use of the lateral line to detect motion and vibrations. (Froese, 2008; Sempier, 2003)

Food Habits

Wolf-eels use their robust jaws and teeth to eat hard-shelled invertebrates, such as crabs up to 114 mm in width, snails, sand dollars, sea urchins, mussels, clams, and abalone, especially Haliotis kamtschatkana. In the Monterey area the dominant food items are slender crabs (Cancer gracilis) and sand dollars (Dendraster excentricus). Wolf-eels occasionally eat fish as well, although they seem best able to capture slow-moving prey. (Emmet and Jamieson, 1988; Froese, 2008; Hulberg and Graber, 1980; Sempier, 2003; Waldron, 1958)

  • Animal Foods
  • fish
  • mollusks
  • aquatic crustaceans
  • echinoderms

Predation

Wolf-eel eggs are eaten by rockfish (Sebastes species) and kelp greenlings (Hexagrammos decagrammus). Wolf-eels aggressively defend their territories. When threatened, they approach the threat with the mouth held open, displaying the teeth. (Sempier, 2003)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Wolf-eels are important predators of marine invertebrates, especially crabs, mollusks, and echinoderms. (Froese, 2008; Hulberg and Graber, 1980; Sempier, 2003)

Economic Importance for Humans: Positive

Wolf-eels are considered good to eat and are taken for food by humans. There are small-scale commercial fisheries that take wolf-eels and they are considered a potential species useful in aquaculture. Wolf-eels are kept in zoos and aquariums, although they are difficult to keep and may be aggressive. (Froese, 2008; Sempier, 2003)

  • Positive Impacts
  • food
  • research and education

Economic Importance for Humans: Negative

Wolf-eels have robust jaws and teeth and can inflict a painful bite if disturbed, although they seem to rarely attack unless severely provoked. (Froese, 2008; Hulberg and Graber, 1980)

  • Negative Impacts
  • injures humans
    • bites or stings

Conservation Status

Wolf-eels have not been evaluated by the IUCN red list. Several of their close relatives, species of wolfish (Anarichas), are considered threatened or species of concern by the Canadian Species at Risk program, prompting recent genetic research on this group. In coastal California, reports suggest wolf-eel populations are large, but no systematic survey is reported. (Hulberg and Graber, 1980; Johnstone, et al., 2007)

Other Comments

The generic name comes from the Greek anarrhichesis, meaning to climb. (Froese, 2008)

Contributors

Tanya Dewey (author), Animal Diversity Web.

Glossary

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

benthic

Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

food

A substance that provides both nutrients and energy to a living thing.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

molluscivore

eats mollusks, members of Phylum Mollusca

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

piscivore

an animal that mainly eats fish

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

References

Beamish, R., K. Leask, O. Ivanov, A. Balanov, A. Orlov, B. Sinclair. 1999. The ecology, distribution, and abundance of midwater fishes of the Subarctic Pacific gyres. Progress in Oceanography, 43: 399-422.

Emmet, B., D. Jamieson. 1988. An experimental abalone transplant project in Barkley Sound, British Columbia. Fisheries Bulletin, 87: 95-104.

Feeney, R., R. Lea, S. Dyer, S. Gietler. 2007. First Record of the Wolf-Eel, Anarrhichthys ocellatus (Pisces: Anarhichadidae), from Baja California, Mexico. California Fish and Game Scientific Journal, 93: 52-55.

Froese, R. 2008. "Anarrhichthys ocellatus (wolf-eel)" (On-line). fishbase.org. Accessed January 28, 2009 at http://www.fishbase.org/summary/speciessummary.php?id=3813.

Hulberg, L., P. Graber. 1980. Diet and behavioural aspects of the wolf-eel Anarrhichthys ocellatus, on sandy bottom in Monterey. California Fish and Game Scientific Journal, 66: 172-177.

Johnstone, K., H. Marshall, S. Carr. 2007. Biodiversity genomics for species at risk: patterns of DNA sequence variation within and among complete mitochondrial genomes of three species of wolffish (Anarhichas spp.). Canadian Journal of Zoology, 85: 151-158.

Sempier, S. 2003. "Wolf Eel" (On-line). Marine Species with Aquaculture Potential, Oregon State University. Accessed January 29, 2008 at http://hmsc.oregonstate.edu/projects/msap/PS/masterlist/fish/wolfeel.html.

Waldron, K. 1958. The fishery and biology of the Dungeness crab (Cancer magister Dana) in Oregon waters. Contributions of the Oregon Fish Commission, 24: 1-20.