How to Identify Blue Threadfin Salmon

To identify Blue Threadfin Salmon (Eleutheronema tetradactylum), look at these key features.

Physical Characteristics

Body shape

elongated

Coloration

Silvery-blue to silvery-grey dorsally, fading to white or pale silver ventrally. Fins are typically dusky or yellowish, sometimes with darker margins. The free pectoral fin rays are often whitish or yellowish.

Scale type

ctenoid

Mouth position

terminal

Distinctive features

Four prominent, long, free pectoral fin rays on each side, extending well beyond the origin of the pelvic fins, sometimes reaching the caudal fin base., Two distinct dorsal fins; the first with 8 spines, the second with 1 spine and 13-15 soft rays., Deeply forked caudal fin., Large, prominent eyes., Snout projects slightly beyond the mouth.

Dorsal fin

Two dorsal fins: first dorsal fin with 8 spines; second dorsal fin with 1 spine and 13-15 soft rays. The second dorsal fin is typically longer than the first.

Tail fin

Deeply forked caudal fin with pointed lobes.

Pectoral fin

Pectoral fins are located low on the body, with the upper rays branched and the lower 4 rays completely free and elongated. These free rays are crucial for sensory perception and foraging.

Distinctive fins

Pelvic fins are thoracic, located below the pectoral fins. Anal fin has 3 spines and 13-16 soft rays, similar in shape and size to the second dorsal fin.

Identification Tips

1. 1

   Free Pectoral Fin Rays

   The most distinguishing feature is the presence of four long, free, filamentous rays below the main pectoral fin. These are tactile organs used to locate prey in murky waters.

2. 2

   Body Coloration

   A generally silvery body with a bluish or greyish tinge on the back, fading to white on the belly. Fins are often dusky or yellowish.

3. 3

   Dorsal Fins

   Two distinct dorsal fins, with the second being noticeably longer than the first.

4. 4

   Snout

   The snout projects slightly beyond the mouth, which is characteristic of many threadfin species.

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