Blue Tangs are often found roaming the reef, in search of their favourite food – algae. They are surgeonfish which may appear either singly or in large schools, which can contain hundreds of individuals.

The name surgeonfish comes from the defensive spines located on the caudal peduncle (the part of the fish between the tail and the rest of the body) which are as sharp as a surgeon’s scalpel. They are herbivorous, eating plants and algae, so their spines are used only for defense.

Blue Tangs are sometimes found schooling with other members of the surgeonfish family. These schools form around dusk when nocturnal predators, such as moray eels, begin to hunt. These schools provoke an aggressive reaction from the smaller damselfishes defending patches of algae.

The true Blue Tang is Acanthurus coeruleus, which found in the Caribbean Sea. Other fish are also sometimes referred to as Blue Tang. In the Red Sea, for example, there is Zebrasoma xanthurum, more properly known as Yellowtail Tang. Also in the Indo-Pacific masquerading as Blue Tang is the Palette Surgeon, Paracanthurus hepatus; familiar if you’ve watched the “Finding Nemo” film.

As you might expect, blue tangs are largely blue. The Caribbean Blue Tang, Acanthurus coeruleus, has a bright yellow or white spine. It lives between 3 and 28 m on rocky or coral reefs. As it is unafraid of divers you can usually get quite close to it.

The Blue Tang, and other surgeonfish, are important on a shallow coral reef because they help keep the algae in check. Without them the algae would grow so fast that coral larvae settling and trying to make a start on the reef would soon be overgrown.

Further reading:

Beautiful Oceans Coral Reef Architecture & Organisms
,
The Blue Planet

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