How to Identify Pacific Jack Mackerel

To identify Pacific Jack Mackerel (Trachurus symmetricus), look at these key features.

Physical Characteristics

Body shape

torpedo

Coloration

Dorsal side is iridescent blue to greenish-blue, fading to silvery on the flanks and belly. A distinct black spot is often present on the upper margin of the operculum (gill cover).

Scale type

cycloid

Mouth position

terminal

Distinctive features

Two widely separated dorsal fins., A series of 24-40 scutes (bony plates) along the entire lateral line, which are particularly prominent and keeled posteriorly., A small, adipose eyelid covering most of the eye., A small, terminal mouth with minute teeth.

Dorsal fin

First dorsal fin has 8-9 spines; second dorsal fin has 1 spine and 28-33 soft rays, followed by a series of 5-9 finlets (though these are often less distinct than in true mackerels).

Tail fin

Deeply forked caudal fin.

Pectoral fin

Long and falcate (sickle-shaped), extending beyond the origin of the second dorsal fin.

Distinctive fins

Two anal fins, the first with 2 detached spines (often embedded in adults), followed by 1 spine and 24-29 soft rays, also followed by 5-9 finlets.

Identification Tips

1. 1

   Lateral Line Scutes

   The most definitive feature is the complete lateral line armed with a series of prominent, keeled scutes (bony plates) from head to tail. This distinguishes it from true mackerels (Scomber spp.) which lack these scutes.

2. 2

   Dorsal Fins

   Two distinct dorsal fins, with the first being spiny and the second soft-rayed, followed by small finlets. The separation between the two dorsal fins is noticeable.

3. 3

   Opercular Spot

   Presence of a small, distinct black spot on the upper posterior margin of the operculum (gill cover).

4. 4

   Body Shape and Coloration

   Streamlined, silvery body with an iridescent blue-green back. This general appearance is common among pelagic schooling fish, so rely on other features for positive identification.

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