Humu-humu-nuku-nuku-apua-a is a kind of triggerfish. You can see them in aquarium stores some times. Ugly thing with a crescent tail, pouty mouth and a wedge-shaped head. I kind of like them because of the song.

The name means, more or less, "fish that swims along and grunts like a pig." I've never heard one grunt. Maybe they never grunt in captivity.