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Gymnosarda unicolorBonito

By Kevin Samuels

Geographic Range

Dogtooth tuna (Gymnosarda unicolor) are found in the Indo West Pacific, from Australia (the Great Barrier Reef) to East Africa and the Red Sea, and in the waters off of the coast of Japan and the Philippines, New Guinea, Marquesas, Tahiti, Tuamotus, Pitcairn, and Oeno Islands. (Fishbase, 2007)

Habitat

Dogtooth tuna are typically pelagic, but are known to come inshore and are found around coral reefs and atolls at depths from 15m (50ft) to 45m (150ft). They prefer water temperatures between 21°C (70°F) and 26°C (80°F). They are migratory; their movements are linked to water temperatures and the fish they feed upon. (Fishbase, 2007)

Physical Description

Dogtooth tuna are members of the mackerel family. Distinguishing features include a streamlined body with a large head and a mouth that contains twenty sharp dog-like teeth per jaw. They have two dorsal fins; the first is spiny and large, and the second, right behind it is soft-rayed. The ventral fin is similar in size and shaped like the second dorsal. Nine spiny finlets stretch down the upper and lower tail section toward its crescent shaped tailfin. This species exhibits counter shading and has no scales. The dorsal surface is blue green, the sides are silver, and the belly is white. They swim constantly with their mouth open to force water through the gills because of a high oxygen requirement and great muscular activity. An unusual vessel system in the liver and tail provides counter-current temperature exchange, raising the body temperature 6°C to 12°C higher than the water temperature. They can reach speeds of up to 80 kph (50 mph). Dogtooth tuna's average weight is 15 to 20 kg (33 to 44 lbs). The spear fishing record is 55 kg and the all-tackle record is 131kg (288 lbs). (Fishbase, 2007; Grizimek and Ladiges, 1974; Maas, 1997)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    131 (high) kg
    288.55 (high) lb
  • Average mass
    15-20 kg
    lb

Reproduction

Spawning takes place around December, January, and February. Dogtooth Tuna are non-guarders and are classified as open water substratum egg scatterers. The eggs are small and float near the surface, hatching within two days. Larvae are .635cm (0.25 inch) long and grow very quickly. (Fishbase, 2007; Grizimek and Ladiges, 1974)

  • Breeding season
    Spawning takes place from December to February.

Behavior

Dogtooth tuna usually form schools of individuals of the same relative size. Larger fishes are independent, but sometimes swim with Carcharhinus amblyrhynchos (gray reef sharks). When they encounter a school of food fishes in the open ocean, feeding frenzies are not uncommon. Often these frenzies result in injury to other dogtooth tunas. (Maas, 1997)

Communication and Perception

Food Habits

Dogtooth tuna feed upon shoaling fishes like herring (Clupea), sprats (Sprattus), mackerel (Scomber), whiting (Merlucciidae), cuttlefish (Sepia) and sometimes squid (Loligo).

  • Animal Foods
  • fish

Economic Importance for Humans: Positive

Dogtooth tuna are a popular game fish. Many charter-fishing boats operate out of Australia and other parts of the south pacific providing a very lucrative business for their owners. They are also marketed commercially either canned or frozen. (Fishbase, 2007)

Economic Importance for Humans: Negative

Ciguatera Fish Poisoning in humans is caused by the consumption of subtropical and tropical finfish. A naturally occurring toxin found in an algae (dinoflagellate) species common in the lower latitudes is the suspected cause. The occurrence of toxic fish is sporadic, and not all fish of a given species or locality will be toxic. Ciguatera poisoning is self-limiting: symptoms usually subside after a few days, are dismissed as seasickness or a hangover, and are therefore under reported.

Conservation Status

Dogtooth tuna are susceptible to overfishing, and commercial net fishing is their biggest threat. Coupled with worldwide concern over dolphin free tuna, there is hope that this species can be protected with proper management. As yet, they have not made the ICUN red list and are not considered a threatened species. (Fishbase, 2007; Maas, 1997)

Other Comments

Dogtooth tuna meat is whiter than that of other species of tuna, so they are widely sought after and highly prized both by commercial and sport fishermen. (Maas, 1997; Mitting, March 20, 1999)

Contributors

Kevin Samuels (author), Fresno City College, Carl Johansson (editor), Fresno City College.

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.

World Map

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.

diurnal
  1. active during the day, 2. lasting for one day.
ecotourism

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

ectothermic

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

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

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.

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).

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.

nomadic

generally wanders from place to place, usually within a well-defined range.

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

oviparous

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

pelagic

An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).

piscivore

an animal that mainly eats fish

reef

structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

saltwater or marine

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

seasonal breeding

breeding is confined to a particular season

sexual

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

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

References

"Crystal Divers" (On-line). Accessed Sept. 16, 2000 at http://www.crystaldivers.com/gallery24.html.

Fishbase, 2007. "Fishbase" (On-line). Accessed Sept. 21, 2000 at http://www.fishbase.org/Summary/SpeciesSummary.cfm?genusname=Gymnosarda&speciesname=unicolor.

Grizimek, B., W. Ladiges. 1974. Fishes 2. New York, New York: Van Nostrand Reinhold LTD.

Maas, T. 1997. "BlueWater Hunting and Freediving" (On-line). Accessed Sept 16, 2000 at http://www.freedive.net/chapters/dogtooth8.html.

Mitting, C. March 20, 1999. "Fish N Fin in Oz-Dogtooth Tuna" (On-line). Accessed Sept. 16, 2000 at http://www.the-fishing-network.com/magazine/v04/n06/fishnfin.html.

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