Animal Diversity Web

Diversity

The family Scombridae, the mackerels, tunas, and bonitos, includes some of the world’s most popular food and sport fishes. The family also boasts the fastest-swimming fishes in the world, and bluefin tunas are probably the largest of all bony fishes. Scombrids’ size, speed, and popularity are related to their high degree of adaptation to a pelagic, nomadic existence. Their bodies are formed to maximize swimming efficiency, and tunas even have a vascular heat exchange system that allows for prolonged swimming in colder water (see Physical Description). Smaller mackerels often live closer to shore, but other mackerels, tunas, and bonitos roam deeper waters, often in wide migratory patterns (see Habitat). Due to their great range and extensive use as food fish, scombrids bear many common names and have long been familiar to humans. Bonitos, for example, appear in Captain Cook’s journals. Human influence, however, has rendered at least five species endangered or vulnerable to extinction. The family Scombridae is comprised of two tribes, subdivided into 15 genera and 49 species. (Helfman, et al., 1997; Johnson and Gill, 1998; Nelson, 1994; The World Conservation Union, 2002; Wheeler, 1985)

Geographic Range

Tunas, mackerels, and bonitos can be found worldwide in tropical and subtropical seas, with many species traveling periodically into cool temperate waters. (Johnson and Gill, 1998; Nelson, 1994)

• Biogeographic Regions
• nearctic
  • native
• palearctic
  • native
• oriental
  • native
• ethiopian
  • native
• neotropical
  • native
• australian
  • native
• oceanic islands
  • native
• indian ocean
  • native
• atlantic ocean
  • native
• pacific ocean
  • native
• mediterranean sea
  • native

• Other Geographic Terms
• cosmopolitan

Habitat

Scombrids are, for the most part, pelagic (open-ocean) fishes living in tropical and subtropical seas. Some species make seasonal forays into cool temperate or cold waters. Some, especially the smaller mackerels, remain near coastlines, while many others roam deeper waters. They are a marine family, although some groups occur in brackish water, and one normally marine species, Scomberomorus sinensis, has been found in fresh water 300 km up the Mekong River. Many groups within Scombridae tend to remain near the surface and over the continental shelf. (Helfman, et al., 1997; Johnson and Gill, 1998; Nelson, 1994; Wheeler, 1985)

• Habitat Regions
• temperate
• tropical
• saltwater or marine
• freshwater

• Aquatic Biomes
• pelagic
• coastal
• brackish water

Physical Description

Scombrids (tunas, mackerels, and bonitos) have streamlined bodies that taper on either end, moderately large mouths, and well-developed teeth. Gill membranes are not attached to the isthmus. Scales are cycloid and usually tiny, and body coloration is metallic, often blue and silver. Spanish mackerels have yellow to bronze spots and bonitos and tunas may have dusky bands and fins. The dorsal fin is composed of nine to 27 densely packed rays, and the pelvic fins have six rays. One member of the family, bluefin tuna, can reach 4.2 m and are probably the world’s largest bony fishes. Scombrids are highly adapted to continuous swimming in the open ocean. Their bodies are an ideal streamlined shape, with the thickest part of the body occurring two-fifths of the way back from the head. Their dorsal fins can slot into grooves to reduce drag, and the caudal fin is stiff and sickle-shaped for powerful propulsion. The five to 12 separate finlets behind the anal and second dorsal fins may allow the tail to push against less turbulence by preventing vortices from forming in water flowing toward the tail. The slender caudal peduncle bears at least two keels that reduce drag and may accelerate water flowing over the tail. (Click here to see a fish diagram). (Allen and Robertson, 1994; Böhlke and Chaplin, 1968; Helfman, et al., 1997; Johnson and Gill, 1998; Nelson, 1994; Wheeler, 1985)

Tunas are negatively buoyant and must swim continuously to avoid sinking. In addition, they require constant movement to ventilate the gills. Through a process called ram gill ventilation, swimming (at speeds no less than 65 cm per second) forces water over the gills. Tunas have numerous lamellae (gill membranes) and very thin lamellar walls, and are able to extract more oxygen from the water than any other fish. Tunas have large hearts and blood volumes. They also have a high proportion of the red muscle that permits sustained swimming, buried centrally along the spinal column to conserve heat. Other members of the family, such as the mackerels, also have red muscle, but located nearer the outside of the fish. (Helfman, et al., 1997; Johnson and Gill, 1998)

One of the most striking features of the scombrids is that some groups are endothermic, able to maintain a body temperature higher than that of the surrounding water. Tunas (tribe Thunnini) conserve heat produced by swimming muscles through an arrangement of blood vessels called a rete mirabile (“wonderful net”). These blood vessels act as a countercurrent heat-exchanger. In any fish, when blood cycles through the gills to receive oxygen, it also cools to the temperature of the surrounding water. In tunas, this blood is diverted to vessels near the outside of the body instead of traveling directly through the fish’s core. Before flowing inward, the cool, oxygenated blood passes through a network of small vessels, countercurrent to warm blood leaving the swimming muscles, and heat is transferred to the entering blood. In this way much of the heat generated by swimming muscles is conserved. In waters ranging from 7 to 30˚ C, bluefin tuna maintain muscle temperatures between 28 and 33 C. Others keep body temperatures 3 to 7 degrees C warmer than the surrounding water. Some species, such as bigeye tuna, utilize the heat exchanger only when they enter colder water. Endothermy also helps warm parts of the central nervous system, which stabilizes nervous system function in cold water. Butterfly mackerels keep brain and eye temperatures elevated using thermogenic (heat-producing) tissue. (Click here to see a diagram of tuna thermoregulation). (Allen and Robertson, 1994; Helfman, et al., 1997; Johnson and Gill, 1998; Moyle and Cech, 2000; Nelson, 1994; Wheeler, 1985)

• Other Physical Features
• endothermic
• heterothermic
• bilateral symmetry

Development

Carried by the same current system as adults, scombrid larvae and juveniles grow and feed along with mature individuals. In at least one species, Atlantic mackerel, eggs hatch in two to five days depending on the temperature. Mackerel grow quickly and can reach 24 cm in a year. (Helfman, et al., 1997; Wheeler, 1985)

Reproduction

No information was found regarding mating systems in Scombridae.

Scombrids, with the exception of bluefin tunas, spawn repeatedly. Some, like Scomber scombrus (Atlantic mackerel), spawn all summer long. Female mackerels produce, on average, about half a million eggs, which float near the surface. Bluefin tunas spawn in tropical waters of the Gulf of Mexico, and spend the rest of the year feeding in temperate regions. (Helfman, et al., 1997; Wheeler, 1985)

• Key Reproductive Features
• iteroparous
• seasonal breeding

No information was found regarding parental care in Scombridae.

Lifespan/Longevity

No information was found regarding lifespan of fishes in Scombridae.

Behavior

Most scombrids are schooling fishes, but some can be found singly. They follow a nomadic lifestyle, sometimes making migrations of huge distances. For some groups, migrations are seasonal and may be determined by water temperature. Scombrids are continuous swimmers, and tunas in particular have a unique, efficient swimming style (called thunniform), in which the body remains stiff while the thin tail oscillates quickly. Some species of bonito (in the genus Sarda) habitually leap clear of the water when pursuing prey. (Helfman, et al., 1997; Wheeler, 1985)

• Key Behaviors
• natatorial
• motile
• nomadic
• migratory
• social

Communication and Perception

No information was found regarding communication in Scombridae.

• Perception Channels
• visual
• tactile
• chemical

Food Habits

Scombrids are active predators that feed on a wide range of organisms. The diet of a single species may include crabs, shrimps, squids, crustaceans, the larvae of fishes and invertebrates, and fishes several feet long. Some smaller species strain zooplankton through their gill rakers. Tunas feed on a variety of mid-water and surface fishes, with mackerel providing a favorite meal. Tunas’ ability to maintain elevated body temperatures enables them to swiftly pursue prey in the cold waters of deeper depths and higher latitudes. Migratory tunas have the fastest digestion rates and highest metabolic rates of any fish. (Böhlke and Chaplin, 1968; Froese, et al., 2003; Helfman, et al., 1997; Wheeler, 1985)

• Primary Diet
• carnivore
  • piscivore
  • eats non-insect arthropods

Predation

Some of the smaller species, such as Scomber japonicus, are food for a large number of predators, from fishes and porpoises to seals and seabirds. Mackerels are fed upon by large tunas, other large fishes, and sharks. Tunas, even large ones, must watch out for the temperate and warm temperate swordfish Xiphias gladius and other tropical sailfishes, spearfishes and marlins (Istiophorus, Tetrapturus, Makaira). Humans are a predator shared by all the scombrids. (Helfman, et al., 1997; Wheeler, 1985)

• Known Predators

  • tuna (Scombridae)
  • swordfishes (Xiphias)
  • spearfishes (Istiophoridae)
  • marlins (Istiophoridae)
  • sharks (Chondrichthyes)
  • porpoises (Phocoenidae)
  • seals (Phocidae)
  • seabirds (Aves)
  • humans (Homo sapiens)

Ecosystem Roles

Scombrids are major predators in pelagic habitats. As such they impact the populations of the many organisms on which they feed, from zooplankton to fish larvae to large fish. They, in turn, provide food for each other, large fishes, porpoises, seals, and seabirds. (Böhlke and Chaplin, 1968; Helfman, et al., 1997; Wheeler, 1985)

Economic Importance for Humans: Positive

Most scombrids (tunas, mackerels, and bonitos) are important food, commercial, and sport fishes. In some parts of the world, i.e. the Mediterranean and Californian coasts, tunas have been fished locally for many years, but heavy commercial exploitation of open-ocean tunas has led in some cases to depletion of tuna populations. Much of the tuna catch is harvested for canning. Apparently the flesh of king mackerel has occasionally been toxic when eaten. (Wheeler, 1985)

• Positive Impacts
• food

Economic Importance for Humans: Negative

No specific information was found concerning any negative impacts to humans.

Conservation Status

As of 1994 there were several threatened species in Scombridae. Scomberomorus concolor (Monterrey Spanish mackerel) was listed as endangered, and Thunnus maccoyyii (southern bluefin tuna) as critically endangered; in other words both face severe threat of extinction. Thunnus obesus (bigeye tuna) was listed as vulnerable, and two others, Thunnus alalunga (albacore tuna) and Thunnus thynnus (northern bluefin tuna) may be threatened as well. (The World Conservation Union, 2002)

• IUCN Red List [Link]

  Not Evaluated

Other Comments

The fossil record for Scombridae dates back to the lower Tertiary and lower Eocene. (Berg, 1958)

Contributors

Monica Weinheimer (author), Animal Diversity Web.

References

Allen, G., D. Robertson. 1994. Fishes of the Tropical Eastern Pacific. Honolulu, HI: University of Hawaii Press.

Berg, L. 1958. System Der Rezenten und Fossilen Fischartigen und Fische. Berlin: VEB Deutscher Verlag der Wissenschaften.

Böhlke, J., C. Chaplin. 1968. Fishes of the Bahamas and Adjacent Tropical Waters. Wynnewood, PA: Published for the Academy of Natural Sciences of Philadelphia by Livingston.

Froese, R., D. Pauly, D. Woodland. 2003. "Fish Base" (On-line). FishBase World Wide Web electronic publication. Accessed September 16, 2003 at http://www.fishbase.org/.

Helfman, G., B. Collete, D. Facey. 1997. The Diversity of Fishes. Malden, MA: Blackwell.

Johnson, G., A. Gill. 1998. Perches and Their Allies. Pp. 190 in W Eschmeyer, J Paxton, eds. Encyclopedia of Fishes – second edition. San Diego, CA: Academic Press.

Kuiter, R. 1993. Coastal Fishes of South-Eastern Australia. Honolulu, HI: University of Hawaii Press.

Moyle, P., J. Cech. 2000. Fishes: An Introduction to Ichthyology – fourth edition. Upper Saddle River, NJ: Prentice-Hall.

Nelson, J. 1994. Fishes of the World – third edition. New York, NY: John Wiley and Sons.

The World Conservation Union, 2002. "IUCN 2002" (On-line). 2002 IUCN Red List of Threatened Species. Accessed September 16, 2003 at http://www.iucnredlist.org/.

Wheeler, A. 1985. The World Encyclopedia of Fishes. London: Macdonald.