How to Identify Smallmouth Jack

To identify Smallmouth Jack (Caranx bucculentus), look at these key features.

Physical Characteristics

Body shape

compressed

Coloration

Dorsal surface is typically bluish-green to silvery-blue, fading to silvery-white on the ventral side. Juveniles and subadults often exhibit 5-7 dark vertical bands on their flanks, which fade with age. Adults are characterized by numerous small, iridescent blue spots scattered over the upper half of their body, particularly prominent on the operculum and anterior flanks. Fins are generally dusky to yellowish, with the caudal fin often yellowish.

Scale type

cycloid

Mouth position

terminal

Distinctive features

Relatively small, terminal mouth that does not extend past the anterior margin of the eye., Deep, compressed body., Prominent blue spots on the upper flanks and operculum of adults., Strongly curved lateral line anteriorly, becoming straight posteriorly., Scutes present on the posterior straight section of the lateral line, typically 30-40 strong scutes.

Dorsal fin

Two dorsal fins; the first with 8 spines, the second with 1 spine and 20-23 soft rays. The anterior lobe of the second dorsal fin is moderately elevated.

Tail fin

Deeply forked caudal fin with pointed lobes.

Pectoral fin

Long, falcate (sickle-shaped) pectoral fins, longer than the head.

Distinctive fins

Anal fin with 2 detached spines followed by 1 spine and 16-19 soft rays. The anterior lobe of the anal fin is also moderately elevated, similar to the second dorsal fin.

Identification Tips

1. 1

   Mouth Size

   The most distinguishing feature is its relatively small mouth. The maxilla typically does not extend past the anterior margin of the eye, unlike many other Caranx species where it extends to or beyond the middle of the eye.

2. 2

   Blue Spots

   Adults possess numerous small, iridescent blue spots on the upper half of the body, particularly noticeable on the operculum and anterior flanks. This is a key identifier.

3. 3

   Body Depth

   It has a relatively deep body compared to some other jacks, with a body depth typically 2.5-2.9 times in standard length.

4. 4

   Lateral Line Scutes

   Count the scutes on the straight posterior section of the lateral line; Caranx bucculentus typically has 30-40 strong scutes.

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