Scales on a fish provide protection. Hard, sturdy and slippery scales prevent damage from sharp objects like coral, and they protect the fish from predators' sharp teeth.
Scales are bony and overlap, which not only protects the fish, but allows a gliding side-to-side swimming motion. The porcupine fish raises its scales to ward off predators. A shark's scales resemble teeth. Catfish and lamprey do not have scales. In addition to scales, fish have two layers of skin. The outer epidermis produces a slimy substance to ward off fungi and bacteria. The inner skin is tough and bony. Rings on a fish scale indicate its age.