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How to Identify the Bluefin Tuna

The Atlantic bluefin tuna, Thunnus thynnus, is the biggest member of a family of fishes that includes species such as mackerel and albacore as well. The bluefin tuna, nicknamed the horse mackerel, has a wide range across the Atlantic, occurring off North America in the ocean from Labrador to as far south as northeastern Brazil, according to the "National Audubon Society Field Guide to Fishes. A powerful swimmer, this tuna, prized for the fight it gives an angler and for its flesh, has specific characteristics and behaviors that help identify it.

Instructions

- 1
  Look for a fish that achieves lengths up to 14 feet in the largest of specimens, but is typically about 6 ½ feet long when mature. The average weight of the bluefin tuna is about 550 lbs., states the National Oceanic and Atmospheric Administration. Individuals weighing close to 1,500 lbs, are on record, but are extremely rare due to the pressure put on this species by constant fishing.
- 2
  Examine the coloring of the bluefin tuna, studying its top portion (dorsal) versus the shades on its bottom portion (ventral). The upper surface of the bluefin tuna is dark blue or blackish, while the ventral region is usually a silvery white hue.
- 3
  Study the two dorsal fins on the bluefin tuna, observing their color and texture. The first dorsal fin is blue or yellowish, while the one situated behind it is a reddish shade of brown. The first dorsal fin is harder, composed normally of 14 spines, but on occasion comprised of just 12 or 13. The second dorsal fin of the bluefin tuna features between 13 and 15 much softer rays, notes Marine Bio.
- 4
  Observe the shape of the snout of the bluefin tuna. It is conical and appears much smaller than the rest of the head. The lower jaw of this fish extends back to be even with the midsection of the tuna's eye above it.
- 5
  Identify the bluefin tuna from its behaviors. This fish can swim as rapidly as 45 miles per hour in the open ocean, where it lives to depths up to 650 feet. It is a migratory species, feeding upon other fish, crustaceans, eels and squid. Watch for them to occur in schools, with these groups predicated on the size of the bluefin tuna -- like sizes roam the ocean together in search of food.

Nature