sur·geon·fish 
(sûrjən-fĭsh′)
(sûrjən-fĭsh′)n. pl. surgeonfish or sur·geon·fish·es
Any of various brightly colored tropical marine fishes of the family Acanthuridae, having a laterally compressed body with one or more sharp erectile spines near the base of the tail, and often kept in home aquariums. Also called tang.
[From its lancetlike spines, which resemble surgeons' instruments.]