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Interesting Facts and Information on Bigeye Tuna
(Thunnus obesus)

Bigeye tuna can dive deeper than other tuna species and exhibit extensive vertical movements. This species exhibits clear daily patterns, moving to deeper waters during the daytime...

Interesting Facts about Bigeye Tuna:

Bigeye tuna can dive deeper than other tuna species and exhibit extensive vertical movements. This species exhibits clear daily patterns, moving to deeper waters during the daytime

Bigeye tuna is caught mostly in tropical waters.

In the Atlantic Ocean, the record for the largest bigeye tuna caught recreationally is a 375 pound fish with a fork length of 6.75 feet taken off Ocean City, Maryland in 1977.

Bigeye tuna are believed to have recently evolved from a common parent stock of yellowfin tuna.

Bigeye Tuna live longer than yellowfin tuna. The big-eye tuna has a lifespan of up to 12 years reaching sexual maturity at around four years.

The main predators of bigeye tuna are large billfish and toothed whales.

Bigeye tuna dive deep with the moon.


Did you know?
Tuna cannot pump water over their gills like other fish, instead they swim with their mouths open which forces the water over their gills. If they stop swimming they will suffocate.

Did you know?
Tuna have hearts that are much larger than other fish, they are about 10 times as large, relative to the size of the body.

Mature bigeye tuna spawn at least twice a year; releasing between an incredible 2.9 million and 6.3 million eggs each time.

Big Eye Tuna Information:

Geographic range: Bigeye tuna is found in the Atlantic, Pacific, and Indian oceans in warmer temperature waters between 55 and 84 F. In the western Atlantic, they can be found from Nova Scotia to Argentina, including the Caribbean and the Gulf of Mexico.

Habitat: Bigeye tuna are a pelagic species - they are found from the surface to about 800 feet deep. Larvae are found in tropical waters, but as juvenile fish grow larger, they tend to move into temperate waters.

Life span: Bigeye tuna can live longer than 9 years.

Food: Bigeye tuna feed at night and during the day on fishes, squid, and crustaceans found from the surface to a depth of 500 feet. They favor shrimp, mackerel, and other small tuna.

Growth rate: Relatively fast.

Maximum size: Bigeye typically range in length from 1.5 to 5.5 feet. Bigeye over 6.5 feet are rare.
Reaches reproductive maturity: At about age three and a half.

Reproduction: Mature bigeye spawn at least twice a year. Females can have from 2.9 million to more than 6 million ova. The Gulf of Guinea, off the west coast of Africe, is a major nursery ground for Atlantic bigeye.

Spawning season: Throughout the year when the environment is favorable, and peaking in summer months.

Spawning grounds: In tropical waters.

Migrations: Bigeye tuna are highly migratory. Juvenile and small adult bigeye tuna form schools mostly mixed with other tunas such as yellowfin and skipjack, especially in warm waters. These schools are often associated with drifting objects, whale sharks, and sea mounts.

Predators: The main predators of bigeye tuna are large billfish and toothed whales.

Commercial or recreational interest: Both

Distinguishing characteristics: Bigeye tuna is dark metallic blue on the back and upper sides with white lower sides and belly. The first dorsal fin is deep yellow, the second dorsal and anal find are brownish or yellowish with narrow black edges, and the finlets are bright yellow with broad black edges. Their bodies are stocky and robust, and adults' eyes are large.


Bigeye Tuna or Yellowfin Tuna - How to tell the difference:
By Steve Ross, owner and operator of the boat, Bad Dog, Ensenada, B.C., Mexico.

Bigeye tuna are believed to have recently evolved from a common parent stock of yellowfin tuna.

One of the most difficult fish identification jobs is distinguishing between a Bigeye Tuna (Thunnus obesus) and a Yellowfin Tuna (Thunnus albacares).

There are two methods of examining these fish, exterior and interior. Only the interior examination is 100 percent foolproof. The smaller the size of the tuna, the less effective the exterior examination becomes. The easiest method is to look for first for the characteristics of the Bigeye Tuna first, and by the process of elimination, wind up by concluding you are holding a Yellowfin Tuna.

Exterior Characteristics of a Bigeye Tuna (Thunnus obesus):

1. The Bigeye Tuna's pectoral fins may reach to the second dorsal fin, but are shorter than the Yellowfin Tuna's. A very short pectoral fin indicates that the fish more than likely is a Bluefin Tuna. A very long pectoral fin that reaches beyond the anal fin belongs to an Albacore.

2. There are 18 to 22 gill rakers on the first gill arch of a Bigeye Tuna. There will be 24 to 28 gill rakers on a Bluefin Tuna, and 27 to 33 gill rakers on a Yellowfin Tuna.

3. On a Bigeye Tuna, two dorsal fins are closer together and shorter than on a Yellowfin Tuna. The forward dorsal fin of a Bigeye Tuna has 13 to 14 spines and the rear dorsal fin has 14 to 16 rays.

4. The Bigeye Tuna has a strong lateral keel, between two small keels, located slightly farther back on the tail, on either side of the caudal peduncle.

5. Except for the anterior corselet, the scales of a Bigeye Tuna are small.

6. The Bigeye Tuna's rear dorsal fin is dark brown and edged in black, lacking any yellow.

7. The finlets of the Bigeye Tuna are bright yellow with narrow black edges.

8. Upon expiring, the body of a Bigeye Tuna loses most of its coloration, including the disappearance of its yellow coloration. The dorsal and anal finlets' yellow coloration turns brown after death.

9. The Bigeye Tuna's anal fin is wider and shorter than the Yellowfin Tuna's, and it is colored all silver, with a fringe of yellow and 11 to 15 rays. In a yellowfin tuna the anal fin is long and narrow and only silver in the middle.

10. The corselet (the front area of enlarged scales) of a Bigeye Tuna extends further back than on a Yellowfin Tuna. These front scales are larger up front on both tunas and become smaller along the flanks, which make these tuna appear darker up front. These larger scales cover the fish from the first dorsal fin down around the pectoral fins, and to the ventral fins and then takes a sharp angle backwards. This front area of scales extends further back on a Bigeye Tuna than on a Yellowfin Tuna, all the way to the end of the second dorsal fin. The pectoral fin of a Bigeye Tuna will not cover this extension of scales, while on a Yellowfin Tuna these scales extend barely as far as the second dorsal fin and the pectoral fin will completely cover these scales.

11. The tail of a Bigeye Tuna does not have a white trailing edge. An Albacore's tail has a white trailing edge.

12. The white spots prevalent in small Bigeye Tuna elongate as the fish becomes older.

Interior Characteristics of a Bigeye Tuna (Thunnus obesus):

1. Without a doubt, positive identification of a Bigeye Tuna can be completed by examining its liver. The Bigeye Tuna has a grooved liver with clearly visible striations (fine lines looking like streaks), or dark blood vessels on the margins of the lobes. There are two lobes that are both of the same size. However in the yellowfin tuna these smooth lobes are devoid of these striations and the right lobe is clearly longer than the left lobe or the middle lobe.

See Also:
Information on Bigeye

Big Eye Tuna Facts

Angling | Fishing for Bigeye Tuna

Cooking Bigeye Tuna & Tuna Recipes

Commercial Fishing for Bigeye Tuna



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