Naso tonganus

Naso tonganus, commonly known as the bulbnose unicornfish, is a very large unicornfish which needs plenty of swimming space. It can be aggressive towards other fish, especially tangs and food competitors, but does live in schools, so conspecifics are usually ignored. 

Like other unicornfish, it will eat zooplankton, especially when adult, but it's important it can graze on algae/seaweed the entire day when it is still young, to ensure it will stay healthy. So feed flakes/pellets multiple times a day and make sure there is always seaweed available.