How to Identify Japanese Jack Mackerel

To identify Japanese Jack Mackerel (Trachurus japonicus), look at these key features.

Physical Characteristics

Body shape

torpedo

Coloration

Dorsal side is typically bluish-green to dark green, fading to silvery-white on the flanks and belly. A distinct black spot is present on the upper margin of the operculum.

Scale type

ctenoid

Mouth position

terminal

Distinctive features

Large eyes relative to head size., Two dorsal fins: the first with 8 spines, the second with 1 spine and 27-31 soft rays., Anal fin with 2 detached spines followed by 1 spine and 23-27 soft rays., Lateral line strongly arched anteriorly, becoming straight posteriorly, with 69-73 scutes (bony plates) along the straight portion., Pectoral fins are long and falcate (sickle-shaped).

Dorsal fin

Two dorsal fins; first with 8 spines, second with 1 spine and 27-31 soft rays.

Tail fin

Deeply forked caudal fin.

Pectoral fin

Long and falcate, extending beyond the origin of the second dorsal fin.

Distinctive fins

Two detached spines anterior to the anal fin.

Identification Tips

1. 1

   Lateral Line Scutes

   Count the scutes (bony plates) along the straight posterior portion of the lateral line; Trachurus japonicus typically has 69-73 scutes, which are prominent and keeled.

2. 2

   Opercular Spot

   Look for a distinct black spot on the upper margin of the operculum (gill cover).

3. 3

   Eye Size

   The eyes are relatively large, a characteristic feature of many Trachurus species.

4. 4

   Pectoral Fin Length

   Observe the length of the pectoral fin; it is notably long and falcate, often reaching past the origin of the second dorsal fin.

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