How to Identify Japanese Scad

To identify Japanese Scad (Decapterus maruadsi), look at these key features.

Physical Characteristics

Body shape

torpedo

Coloration

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

Scale type

cycloid

Mouth position

terminal

Distinctive features

Elongated, fusiform body, slightly compressed., Adipose eyelid well developed, covering most of the eye except for a central slit., Lateral line with a distinct arch over the pectoral fin, becoming straight posteriorly., Scutes (enlarged, keeled scales) present along the straight posterior part of the lateral line, numbering 30-40., A detached finlet posterior to the dorsal and anal fins.

Dorsal fin

Two dorsal fins; the first with 8 spines, the second with 1 spine and 29-33 soft rays, followed by a single detached finlet.

Tail fin

Deeply forked caudal fin.

Pectoral fin

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

Distinctive fins

Anal fin with 2 detached spines anteriorly, followed by 1 spine and 25-28 soft rays, and a single detached finlet. Pelvic fins small.

Identification Tips

1. 1

   Body Shape and Coloration

   Look for the streamlined, torpedo-shaped body with a metallic blue-green back and silvery belly. The small black spot on the operculum is a key indicator.

2. 2

   Finlets

   The presence of a single detached finlet behind both the dorsal and anal fins is characteristic of Decapterus species.

3. 3

   Lateral Line Scutes

   Count the scutes along the straight posterior part of the lateral line. For D. maruadsi, there are typically 30-40 scutes, which are larger and more prominent than the scales on the rest of the body.

4. 4

   Pectoral Fin Length

   The long pectoral fin, extending past the origin of the second dorsal fin, helps distinguish it from some other scad species.

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