Acanthuridae

Acanthuridae is the family of surgeonfish, tangs, and unicornfish. 
The family includes about 86 living species. It is made up of marine fish living in tropical seas, usually around coral reefs. Many of the species are brightly colored and popular for aquaria.
One of the characteristics of this family is that they have spines on the tail (also known as "thorn tail").
Size.
Most species of the family are of small size, between 15-40 cm (6-15 in), but the genera "Prionorus" or "Naso" can be larger.