Boxfish are the smallest fish in game (or one of the smallest) and they don't eat anything. They come in schools and sometimes not (before Layla levels and in levels 'The Long Pursuit', 'Midnight Snack' and 'Mad House').The 2 kinds of boxfish have no difference but red ones don't appear in Layla levels.
They are slow moving when alone and a bit faster when they come in schools. Like other small fish, they don't give many points.They are preyed on by lionfish, humphead wrasse, cod, pompano, john dorys, tuna, pompanos, leopard sharks and great white sharks. After Madhouse the Intruder invades and they are forced to leave.They appear 13 times in the game or 21 2/3% total.
Boxfish, like most small fish, come in schools. Eating the entire school will give you a school bonus. A school will have all the boxfish the same color.(For example, a school of red boxfish will never have one orange).
If a school of boxfish comes and one or more of them are eaten, you will not get the School Bonus.
Also, if you ate some of the boxfish but some also remained and you eat others of the same color, but not from the same school, you won't get the School Bonus.