How to Identify African Threadfin

To identify African Threadfin (Alectis ciliaris), look at these key features.

Physical Characteristics

Body shape

compressed

Coloration

Silvery-blue to silvery-green dorsally, fading to silvery-white ventrally. Juveniles may have faint vertical bands. The filamentous fin rays are often dark or black.

Scale type

cycloid

Mouth position

terminal

Distinctive features

Highly compressed, deep body, especially in juveniles., Extremely long, filamentous rays on the dorsal and anal fins in juveniles, which can be several times the body length. These shorten and disappear with age., Steeply arched dorsal profile of the head., Small, embedded scales, giving a smooth appearance., Lateral line strongly arched anteriorly, becoming straight posteriorly.

Dorsal fin

Two dorsal fins; the first with 7-8 spines (the first 5-6 are reabsorbed in adults), the second with 1 spine and 18-20 soft rays. Juveniles have 5-6 elongated, filamentous rays from the second dorsal fin.

Tail fin

Deeply forked caudal fin.

Pectoral fin

Long and falcate (sickle-shaped).

Distinctive fins

Anal fin with 2 detached spines followed by 1 spine and 15-17 soft rays. Juveniles have 5-6 elongated, filamentous rays from the anal fin, mirroring the dorsal filaments.

Identification Tips

1. 1

   Juvenile Fin Filaments

   The most striking feature of juveniles is the presence of extremely long, trailing filamentous rays on both the dorsal and anal fins. These can be several times the length of the body and are a definitive identifier.

2. 2

   Body Shape

   Alectis ciliaris has a very deep, laterally compressed body, giving it a diamond-like or kite-like profile, especially when young.

3. 3

   Head Profile

   The head profile is steeply arched, particularly above the eyes.

4. 4

   Adult Appearance

   As they mature, the filamentous fin rays shorten and eventually disappear, and the body becomes more elongated relative to its depth, though still compressed. Adults retain the silvery coloration and deeply forked tail.

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