How to Identify Skipjack Tuna

To identify Skipjack Tuna (Katsuwonus pelamis), look at these key features.

Physical Characteristics

Body shape

torpedo

Coloration

Dorsal side is dark purplish-blue to black, fading to silvery-white on the flanks and belly. The most distinctive feature is the presence of 4 to 6 prominent, dark, longitudinal stripes on the ventral side, which are typically absent on the dorsal surface.

Scale type

ctenoid

Mouth position

terminal

Distinctive features

Robust, fusiform body, slightly compressed laterally., Small, conical teeth., Two dorsal fins, widely separated. The first dorsal fin has 14-16 spines, and the second dorsal fin is followed by 7-9 finlets., Anal fin is followed by 7-8 finlets., Pectoral fins are short, not reaching the interspace between the dorsal fins., Caudal fin is deeply forked with a narrow peduncle and prominent keels., Body is largely scaleless, except for the corselet (a patch of large, thick scales around the pectoral fins and along the lateral line) and the lateral line itself., Swim bladder is absent.

Dorsal fin

Two dorsal fins, widely separated. First dorsal fin with 14-16 spines, second dorsal fin followed by 7-9 finlets.

Tail fin

Deeply forked, lunate caudal fin with a narrow peduncle and prominent keels, indicative of a fast-swimming pelagic fish.

Pectoral fin

Short, not reaching the interspace between the dorsal fins.

Distinctive fins

7-9 dorsal finlets and 7-8 anal finlets posterior to the second dorsal and anal fins, respectively.

Identification Tips

1. 1

   Body Shape and Size

   Typically grows to about 100 cm (39 inches) in fork length and can weigh up to 34.5 kg (76 lbs), though commonly caught at 50-70 cm and 3-5 kg. It has a robust, torpedo-shaped body.

2. 2

   Coloration and Stripes

   The most reliable identifier is the presence of 4 to 6 distinct, dark, longitudinal stripes on the silvery-white belly. These stripes are usually absent on the dark purplish-blue dorsal surface.

3. 3

   Dorsal Fins

   Two dorsal fins, widely separated. The first dorsal fin is spiny and much taller than the second, soft-rayed dorsal fin. Both are followed by a series of small finlets.

4. 4

   Absence of Swim Bladder

   Unlike many fish, Skipjack Tuna lack a swim bladder, requiring them to constantly swim to maintain buoyancy, a characteristic shared with other fast-swimming pelagic species.

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