Photo copyright Tim Nicholson.
Taken in Ras Mohammed, Red Sea.
Barracuda (Sphyraena barracuda).

Barracudas may school as juvenilles but are usually solitary as adults.

They predate on smaller fish and will not attack divers unless provoked, though they may mistake metallic glints as prey.

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Further Reading:
Coral Reef Guide Red Sea, by Robert Myers and Ewald Lieske
The Red Sea, by Andrea Ghisotti
Underwater Photographer , by Martin Edge