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.
Geographic Range
Tunas, mackerels, and bonitos can be found worldwide in tropical and subtropical seas,
with many species traveling periodically into cool temperate waters.
- Biogeographic Regions
- nearctic
- palearctic
- oriental
- ethiopian
- neotropical
- australian
- oceanic islands
- indian ocean
- atlantic ocean
- pacific ocean
- mediterranean sea
- 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.
- 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
).
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.
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
30Ëš 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
).
- 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.
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.
- 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.
- Key Behaviors
- natatorial
- motile
- nomadic
- migratory
- social
Communication and Perception
No information was found regarding communication in Scombridae.
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.
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.
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.
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.
- 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.
Other Comments
The fossil record for Scombridae dates back to the lower Tertiary and lower Eocene.
Additional Links
Contributors
Monica Weinheimer (author), Animal Diversity Web.
- Nearctic
-
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- Palearctic
-
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- oriental
-
found in the oriental region of the world. In other words, India and southeast Asia.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- Ethiopian
-
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- Neotropical
-
living in the southern part of the New World. In other words, Central and South America.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- Australian
-
Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- 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.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- Atlantic Ocean
-
the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- 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.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- cosmopolitan
-
having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.
- 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).
- tropical
-
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
- saltwater or marine
-
mainly lives in oceans, seas, or other bodies of salt water.
- freshwater
-
mainly lives in water that is not salty.
- pelagic
-
An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).
- coastal
-
the nearshore aquatic habitats near a coast, or shoreline.
- brackish water
-
areas with salty water, usually in coastal marshes and estuaries.
- 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.
- 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.
- 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.
- 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).
- seasonal breeding
-
breeding is confined to a particular season
- natatorial
-
specialized for swimming
- motile
-
having the capacity to move from one place to another.
- nomadic
-
generally wanders from place to place, usually within a well-defined range.
- migratory
-
makes seasonal movements between breeding and wintering grounds
- social
-
associates with others of its species; forms social groups.
- visual
-
uses sight to communicate
- tactile
-
uses touch to communicate
- chemical
-
uses smells or other chemicals to communicate
- food
-
A substance that provides both nutrients and energy to a living thing.
- carnivore
-
an animal that mainly eats meat
- piscivore
-
an animal that mainly eats fish
References
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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/ .
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Johnson, G., A. Gill. 1998. Perches and Their Allies. Pp. 190 in 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.
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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.