How to Identify Shortfin scad

To identify Shortfin scad (Decapterus macrosoma), look at these key features.

Physical Characteristics

Body shape

torpedo

Coloration

Dorsal side metallic blue to blue-green, fading to silvery white on the flanks and belly. A small, distinct black spot is present on the upper margin of the operculum. The caudal fin is typically yellowish.

Scale type

cycloid

Mouth position

terminal

Distinctive features

Elongated, slender body, Adipose eyelid well developed, covering most of eye except for a vertical slit over pupil, Lateral line with a long anterior arch and a straight posterior section, Scutes present along the straight part of the lateral line, numbering 24-40, A small, distinct black spot on the upper margin of the operculum, Two separate dorsal fins

Dorsal fin

Two dorsal fins; the first with 8 spines, the second with 1 spine and 28-33 soft rays, followed by a detached finlet of 1 spine and 1 ray.

Tail fin

Deeply forked caudal fin, typically yellowish.

Pectoral fin

Short pectoral fins, shorter than the head length, typically 1/3 to 1/2 of the head length.

Distinctive fins

Anal fin with 2 detached spines anteriorly, followed by 1 spine and 24-28 soft rays, and then a detached finlet of 1 spine and 1 ray. Pelvic fins are small.

Identification Tips

1. 1

   Body Shape

   Look for the distinctly elongated and slender body, which is more streamlined than many other scad species.

2. 2

   Pectoral Fin Length

   The pectoral fins are notably short, usually less than half the length of the head. This is a key distinguishing feature from other Decapterus species.

3. 3

   Opercular Spot

   A small, but clear, black spot on the upper edge of the operculum (gill cover) is consistently present.

4. 4

   Finlets

   Presence of a single detached finlet behind both the dorsal and anal fins.

5. 5

   Lateral Line Scutes

   Count the scutes (hardened scales) along the straight posterior section of the lateral line; there are typically 24-40 in D. macrosoma.

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