How to Identify African Threadfish

To identify African Threadfish (Alectis alexandrina), look at these key features.

Physical Characteristics

Body shape

compressed

Coloration

Silvery-white to silvery-blue dorsally, fading to white or silvery on the flanks and belly. Juveniles may have faint vertical bands. Fins are typically hyaline (clear) to dusky.

Scale type

cycloid

Mouth position

terminal

Distinctive features

Deeply compressed, rhomboidal body shape, especially in juveniles., Extremely elongated, filamentous anterior rays of the dorsal and anal fins in juveniles, which can be several times the body length. These shorten significantly with age., Steeply rising head profile., Lateral line with a strong arch over the pectoral fin, becoming straight posteriorly., No scutes on the lateral line, a key differentiator from many other carangids.

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. Anterior soft rays are greatly elongated in juveniles.

Tail fin

Deeply forked caudal fin.

Pectoral fin

Long, falcate (sickle-shaped) pectoral fins.

Distinctive fins

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

Identification Tips

1. 1

   Body Shape and Filaments

   Look for the very deep, compressed body. In juveniles, the extremely long, trailing filaments from the dorsal and anal fins are unmistakable. These filaments are much shorter or absent in adults.

2. 2

   Lateral Line

   Observe the lateral line; it has a strong arch anteriorly and becomes straight posteriorly, crucially lacking scutes (bony plates) which are present in many other Carangidae.

3. 3

   Head Profile

   Note the steeply rising, almost vertical head profile, especially in larger individuals.

4. 4

   Coloration

   The overall silvery coloration, often with a bluish tint dorsally, is characteristic. Juveniles may have faint dark bands.

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