How to Identify Slender Tuna

To identify Slender Tuna (Allothunnus fallai), look at these key features.

Physical Characteristics

Body shape

torpedo

Coloration

Dorsal surface dark metallic blue to black, fading to silvery-white on the flanks and belly. Fins are generally dark, sometimes with yellowish tinges on the finlets.

Scale type

ctenoid

Mouth position

terminal

Distinctive features

Extremely numerous and long gill rakers (70-80 on the first arch), which are a key diagnostic feature., Relatively large eyes compared to other tuna species., Slender, elongated body form., Absence of striations on the ventral surface, unlike some other tunas., Small, widely spaced scales on the body, with a well-developed corselet of larger scales around the pectoral fin and along the lateral line.

Dorsal fin

Two dorsal fins; the first dorsal fin has 10-13 spines, and the second dorsal fin has 10-14 soft rays, followed by 7-9 finlets. The first dorsal fin is relatively low.

Tail fin

Deeply forked caudal fin, typical of fast-swimming pelagic fish.

Pectoral fin

Pectoral fins are relatively short, not reaching the interspace between the dorsal fins.

Distinctive fins

Anal fin has 10-14 soft rays, followed by 6-8 finlets. Pelvic fins are small.

Identification Tips

1. 1

   Gill Rakers

   The most definitive identification feature is the exceptionally high number of long gill rakers (70-80) on the first gill arch. This is significantly more than any other tuna species.

2. 2

   Body Shape

   Its body is more slender and elongated than most other tuna species, giving it a 'slender' appearance.

3. 3

   Eyes

   Possesses relatively large eyes for a tuna, which can be a helpful, though not definitive, indicator.

4. 4

   Absence of Ventral Striations

   Unlike some other tunas (e.g., Skipjack Tuna), the Slender Tuna lacks dark longitudinal stripes or striations on its belly.

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