How to Identify Blackfin Tuna

To identify Blackfin Tuna (Thunnus atlanticus), look at these key features.

Physical Characteristics

Body shape

torpedo

Coloration

Dorsally, it is dark metallic blue to black, fading to silvery-white on the flanks and belly. A distinctive golden-yellow stripe often runs along the side, though it may be faint or absent in some individuals. The finlets are dusky to yellowish with dark margins.

Scale type

cycloid

Mouth position

terminal

Distinctive features

Smallest of the Thunnus species., Relatively short pectoral fins, not reaching beyond the origin of the second dorsal fin., Black finlets, particularly the anal finlets, which are often dusky or black-edged., A golden-yellow lateral stripe, sometimes prominent.

Dorsal fin

Two dorsal fins; the first is spiny and much lower than the second, which is soft-rayed. Followed by 7-10 dorsal finlets.

Tail fin

Deeply forked caudal fin (lunate), characteristic of fast-swimming pelagic fish.

Pectoral fin

Relatively short, typically not extending beyond the origin of the second dorsal fin.

Distinctive fins

Anal fin is similar in shape to the second dorsal fin, followed by 7-9 anal finlets that are often dusky or black-edged.

Identification Tips

1. 1

   Size

   Smallest true tuna, rarely exceeding 1 meter (39 inches) in length and 20 kg (44 lbs) in weight.

2. 2

   Pectoral Fin Length

   Pectoral fins are relatively short, not reaching past the origin of the second dorsal fin. This distinguishes it from Yellowfin Tuna (Thunnus albacares) and Bigeye Tuna (Thunnus obesus) which have much longer pectoral fins as adults.

3. 3

   Finlet Coloration

   The finlets (especially the anal finlets) are often dusky or black-edged, contrasting with the bright yellow finlets of Yellowfin Tuna.

4. 4

   Lateral Stripe

   Presence of a golden-yellow stripe along the side, though its prominence can vary.

5. 5

   Body Shape

   More robust and less elongated than some other tuna species of similar size.

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