Gymnosarda unicolor

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.

• Biogeographic Regions
• oceanic islands oceanic islands
  • native native
• indian ocean
  • native native
• pacific ocean pacific ocean
  • native native

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.

• Habitat Regions
• tropical tropical
• saltwater or marine saltwater or marine

• Aquatic Biomes
• pelagic pelagic
• reef reef
• coastal coastal

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).

• Other Physical Features
• endothermic endothermic
• ectothermic ectothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike

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.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • external external
• oviparous oviparous

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.

• Key Behaviors
• natatorial natatorial
• diurnal diurnal
• motile motile
• nomadic nomadic
• social social

Communication and Perception

• Perception Channels
• tactile tactile
• chemical chemical

Food Habits

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

• Primary Diet
• carnivore carnivore
  • piscivore piscivore

• 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.

• Positive Impacts
• food food
• ecotourism ecotourism

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.

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.

Additional Links

Encyclopedia of Life

Contributors

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

References

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 .

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