How to Identify Thresher Shark

To identify Thresher Shark (Alopiidae), look at these key features.

Physical Characteristics

Body shape

torpedo

Coloration

Typically dark metallic blue, grey, or brownish-black dorsally, fading to white or cream ventrally. Some species may have metallic reflections.

Scale type

placoid

Mouth position

subterminal

Distinctive features

Extremely long, whip-like upper lobe of the caudal fin, often equal to or longer than the body length., Relatively small mouth with small, curved, blade-like teeth., Large eyes, positioned laterally.

Dorsal fin

Two dorsal fins; the first is large and erect, positioned well forward, while the second is very small.

Tail fin

Highly asymmetrical, with an extraordinarily elongated upper lobe and a much shorter lower lobe. The upper lobe is responsible for the 'threshing' action.

Pectoral fin

Long and falcate (sickle-shaped).

Distinctive fins

The caudal fin is the most distinctive feature, with its elongated upper lobe.

Identification Tips

1. 1

   Caudal Fin Length

   The most defining characteristic is the upper lobe of the caudal fin, which is typically as long as the rest of the shark's body. This is unique among sharks.

2. 2

   Body Shape

   They have a robust, torpedo-shaped body, tapering towards the tail.

3. 3

   Eye Size

   Bigeye Thresher (Alopias superciliosus) has notably larger eyes than the Common and Pelagic Threshers, adapted for hunting in deeper, darker waters.

4. 4

   First Dorsal Fin Position

   The first dorsal fin is relatively large and positioned well forward, usually closer to the pectoral fins than the pelvic fins.

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