My 4 year old fell in love with this fish at the aquarium.
I'm trying to find out what species it is so we can learn more about it.
It looks like a unicornfish (genus Naso), maybe Naso vlamingii, the Bignose Unicornfish. They're Acanthurids, related to surgeonfishes and tangs.
These are mainly found in Indo-Pacific ocean around the depth of 50 mts from surface. Coral reefs are their main habitat and destruction of coral reefs is their current biggest threat alongside trading by fisheries. A good source of information for this species is available here.
A copy of this fish.
Picture credits: UM Rosenstiel School