Alex Hyde / Blue Doctor butterfly (Rhetus periander) drinking salts from mineral-rich river clay, a behaviour know as 'puddling'. On the banks of the Manu River, Manu Biosphere Reserve, Amazonia, Peru. No...

Alex Hyde / Blue Doctor butterfly (Rhetus periander) drinking salts from mineral-rich river clay, a behaviour know as 'puddling'. On the banks of the Manu River, Manu Biosphere Reserve, Amazonia, Peru. No...

Alex Mustard / Blue tang (Acanthurus coeruleus) with Bluehead (Thalassoma bifasciatum) juveniles at cleaning station on coral reef. George Town, Grand Cayman, Cayman Islands, British West Indies. Caribbean Sea. Digi...

Linda Pitkin / Blue tang (Acanthurus coeruleus) and Doctorfish (Acanthurus chirurgus), in foraging aggregation. Bonaire, Leeward Antilles, Caribbean.

Linda Pitkin / Scrawled filefish (Aluterus scriptus) shadowed by Trumpetfish (Aulostomus maculatus). Blue Tang (Acanthurus coeruleus) also in this mixed fish species feeding association. Bonaire, Leeward Antilles,...

Pascal Kobeh / Spanish hogfish (Bodianus rufus) is cleaning a Blue tang surgeonfish (Acanthurus coeruleus) Yucatan Peninsula, Mexico

Claudio Contreras / Blue tang (Acanthurus coeruleus) Yalku inlet, Caribbean Sea, Mexico, February

Claudio Contreras / Blue tang (Acanthurus coeruleus) Yalku inlet, Caribbean Sea, Mexico, February.

Ann & Steve Toon / Elephant Population Management Program surgeon Dr Johan Marais, left, of the University of Pretoria's Faculty of Veterinary Science assisted by Dr Dean Hendrickson, director of Colorado State Universi...

Alex Mustard / Blue tang (Acanthurus coeruleus) portrait, Grand Cayman, Cayman Islands, Caribbean Sea.

Georgette Douwma / Blue tropical reef fish composite image on black background, Blue triggerfish (Pseudobalistes fuscus), Bicolour angelfish (Centropyge bicolor), Elongate surgeonfish (Acanthurus mata), Yellowtail tang...

Pascal Kobeh / A school of Common grunts (Haemulon plumierii) with a few Bluestriped grunts (Haemulon sciurus) and a Blue tang surgeonfish (Acanthurus coeruleus) on the reef with particularly common seafans or gorgo...