How to Identify Diamond Trevally

To identify Diamond Trevally (Monomorphus capricornis), look at these key features.

Physical Characteristics

Body shape

compressed

Coloration

Adults are silvery, often with a bluish or greenish tinge dorsally, fading to silvery-white ventrally. Juveniles have a more silvery body with faint vertical bands and prominent dark spots on the operculum. The filamentous fin rays are typically dark.

Scale type

cycloid

Mouth position

terminal

Distinctive features

Highly compressed, deep body, especially in juveniles., Extremely long, filamentous dorsal and anal fin rays in juveniles, which can be several times the body length. These shorten dramatically with age., Steeply arched dorsal profile of the head., Lateral line strongly arched anteriorly, becoming straight posteriorly, with a posterior section containing 12-30 scutes.

Dorsal fin

Two dorsal fins; the first with 7-8 spines (often embedded in adults), the second with 1 spine and 18-20 soft rays. The anterior soft rays of the second dorsal fin are greatly elongated in juveniles.

Tail fin

Deeply forked caudal fin.

Pectoral fin

Long, falcate pectoral fins.

Distinctive fins

Anal fin with 2 detached spines followed by 1 spine and 15-17 soft rays. Anterior soft rays of the anal fin are also greatly elongated in juveniles, mirroring the dorsal fin.

Identification Tips

1. 1

   Body Shape

   Look for a very deep, compressed body, especially noticeable in juveniles.

2. 2

   Fin Rays

   The most striking feature in juveniles are the extremely long, trailing filamentous rays on the dorsal and anal fins. These are absent or greatly reduced in adults.

3. 3

   Head Profile

   Adults have a distinctly steep and arched head profile.

4. 4

   Scutes

   Presence of scutes (hardened scales) on the posterior straight section of the lateral line, though fewer than many other Carangids (12-30).

5. 5

   Coloration

   Silvery body, sometimes with faint bands in juveniles, and a dark spot on the operculum.

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