The titan triggerfish, Balistoides viridescens, is the largest of the triggerfish species and can grow up to 75 cm in length (30 inches). Their range includes reef areas in the Indo-Pacific region, including Australia, Fiji, Thailand, Indonesia and the Maldives, also in the Red Sea. The fish is not a pelagic species and generally lives in the flat areas of the reef.
Titan triggerfish are the workers of the reef and often surrounded by other fish feeding from the leftovers.Titan triggerfish feed on shellfish, urchins, crustaceans and coral. They are the workers of the reef, often being busy turning over rocks, stirring up the sand and biting off pieces of branching coral. This is why one often sees other smaller fish species around it who feed from the left overs.
The fish can be very aggressive towards divers and snorkellers. Especially during reproduction season it is very territorial and will guard its nest, which it lays in a flat sandy area, vigorously against any intruders. Due to its size and strong teeth it can inflict serious injury. Bites may also be ciguatoxic. The Titan Triggerfish will not always bite, but can swim at snorkellers and divers escorting them out of their territory. When the males (most colourful) start swimming in your direction, the best thing to do is swim away backwards kicking your fins as a defence. Failure to do so may result in being bitten. (text source: wikipedia)