Blackfin Tuna (Thunnus atlanticus)

A member of the Scombridae family and one of the smaller tuna, the blackfin is primarily a sportfish, with minor commercial interest.

Other Names

Bermuda tuna, blackfinned albacore, deep-bodied tunny; French: bonite, giromon, thon nuit; Japanese: mini maguro, monte maguro, taiseiyo maguro; Spanish: albacora, atĂșn aleta negra.

Identification

The pectoral fins of the blackfin tuna reach to somewhere between the twelfth dorsal spine and the origin of the second dorsal fin, but they never extend beyond the second dorsal fin, as in the albacore (see).

There are a total of 19 to 25 (usually 21 to 23) gill rakers on the first arch (15 to 19 are on the lower limb), which is fewer than in any other species of Thunnus. The finlets are uniformly dark, without a touch of the bright lemon yellow usually present in those of other tuna, and they may have white edges.

Light bars alternate with light spots on the lower flanks. The first dorsal fin is dusky; the second dorsal and the anal fins are also dusky, with a silvery luster. The back of the fish is bluish-black, the sides are silvery gray, and the belly is milky white. A small swim bladder is present. The ventral surface of the liver is without striations, and the right lobe is longer than the left and the center lobes.

Size

Blackfin tuna may attain a maximum length of 40 inches, although they are common at about 28 inches and weigh in the 10- to 30-pound range. The all-tackle world record is a 45-pound, 8-ounce Florida fish.

Spawning behavior

The blackfin’s spawning grounds are believed to be well offshore. Off Florida, the spawning season extends from April through November, with a peak in May; in the Gulf of Mexico, it lasts from June through September.

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Food and feeding habits

The diet of blackfin tuna consists of small fish, squid, crustaceans, and plankton. Blackfin often feed near the surface, and they frequently form large mixed schools with skipjacks.

Distribution/Habitat

The blackfin is a pelagic, schooling fish that occurs in the tropical and warm temperate waters of the western Atlantic from Brazil to Cape Cod, including the Caribbean and the Gulf of Mexico. It is most common from North Carolina south and is Florida’s most abundant tuna.
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