How to Identify Jacks, Trevallies

To identify Jacks, Trevallies (Caranx), look at these key features.

Physical Characteristics

Body shape

compressed

Coloration

Typically silvery, often with darker dorsal surfaces and lighter bellies. Some species exhibit iridescent blue, green, or yellow hues, especially on fins or along the lateral line. Juveniles may have vertical bars or spots.

Scale type

cycloid

Mouth position

terminal

Distinctive features

Strongly compressed, deep body, Large, deeply forked caudal fin (tail), Two dorsal fins, the first spiny and the second soft-rayed, Anal fin similar in shape to the second dorsal fin, Prominent scutes (bony plates) along the posterior part of the lateral line, forming a keeled section near the tail, Large eyes, Terminal mouth with small, conical teeth

Dorsal fin

Two dorsal fins; the first with 8 spines, the second with 1 spine and 19-23 soft rays. The anterior rays of the second dorsal fin are often elongated.

Tail fin

Deeply forked, powerful caudal fin, characteristic of fast-swimming pelagic fish.

Pectoral fin

Long, falcate (sickle-shaped) pectoral fins, often extending beyond the origin of the anal fin.

Distinctive fins

Anal fin with 2 detached spines followed by 1 spine and 15-19 soft rays. Pelvic fins are relatively small.

Identification Tips

1. 1

   Body Shape

   Look for the characteristic deep, compressed body and powerful, deeply forked tail.

2. 2

   Lateral Line Scutes

   The presence of a distinct series of bony scutes along the posterior lateral line is a key identifier for Carangidae, and particularly prominent in Caranx.

3. 3

   Fin Morphology

   Note the two dorsal fins (spiny and soft-rayed) and the long, falcate pectoral fins.

4. 4

   Coloration

   While generally silvery, specific species often have unique color patterns, such as the blue fins of the Bluefin Trevally (Caranx melampygus) or the black spot on the operculum of the Crevalle Jack (Caranx hippos).

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