Hopefully the Quick Facts animation on our homepage provided a good introduction to the mighty bluefin tuna - a species at the pinnacle of fish evolution that is often likened to an Olympian of the Oceans - a saltwater Michael Phelps with fins, as it were. This page offers greater detail on the biological traits that make the bluefin tuna so remarkable.

Identification: Bluefin tuna are bullet-shaped, with a crescent moon-shaped tail to provide maximum thrust through the water. Their pectoral, pelvic, and first dorsal fins fold into grooves while swimming to reduce drag. Their backs are dark blue, with a green/yellow iridescence, and their bellies are silver with spots or bands. They have a series of yellow finlets running from the second dorsal fin to the tail, which are edged in black.

As members of the suborder Scombroidei, bluefin are closely related to other tunas, mackerels, bonitos and billfishes. It is sometimes difficult to distinguish bluefin from other tunas, particularly at small sizes. Most notably, the tips of the pectoral fins do not reach the front of the second dorsal fin in bluefin tuna.

The shaded area depicts the known range of Atlantic bluefin. The 45ºW management boundary and two known spawning areas are also shown. (Graphic courtesy of National Research Council)

Size & Age: Atlantic bluefin tuna are among the largest bony fish on earth. The rod and reel world record tipped the scales at 1,496 lbs. in 1979. So-called "giant bluefin" refer to fish greater than 300 lbs. These giants can live up to 30 years. Click here for a table of approximate age at length. Range: Atlantic bluefin tuna are found from the Gulf of Mexico to Newfoundland, Canada in the West Atlantic, and from the Canary Islands off Africa to Iceland in the East Atlantic. While the graphic at left shows the range extending further south, bluefin are thought to have been locally extirpated from those areas. There are at least two separate spawning populations, one in the West Atlantic (i.e., Gulf of Mexico) and one in the East Atlantic (i.e., Mediterranean Sea).

Reproduction: Bluefin tuna are thought to show spawning site fidelity, that is, they return to the place they were born each year to reproduce. The western Atlantic population spawns each late spring/early summer in the Gulf of Mexico.   TAG research has shown that spawning is concentrated in eddies in the western Gulf. Larvae have been recovered in the Florida Straits and Bahamas, suggesting spawning may also be occurring in these regions, but the larvae may have drifted there from the Gulf. The eastern bluefin stock spawns in the Mediterranean Sea, focused around Spain's Balearic Islands and in the Tyrrhenian Sea west of Italy. Interestingly, western bluefin show a median maturation age of 11-12, while the median bluefin tuna spawning age in the Mediterranean is variable and can occur as young as 5 years of age or even earlier. Female bluefin tuna can produce over 10 million eggs in a single spawning season.

The egg-laden ovaries of a ripe female bluefin in the Gulf of Mexico.

Feeding: Bluefin prey upon squid, mackerel, herring, small tuna and other small schooling fish. Whereas young tuna themselves fall prey to many species of seabirds and small fish, giant tuna are preyed upon only by top predators like whales, dolphins, and large sharks.

Did you know? Bluefin can withstand a large range of water temperatures, from 1-31ºC (33-87ºF), because of counter-current heat exchangers that render bluefin endothermic, or warm-blooded, a very rare trait in the fish world. As a result, their body temperature stays stable and warm, even when diving to depths of more than 1,000 m. Amazingly, bluefin can maintain their body temperature up to 70ºF above that of the surrounding water!

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