Most bony fishes have cycloid or ctenoid scales. Both cycloid and ctenoid scal consist of an outer layer of calcium and an inner layer of connective tissue. Cycloid and ctenoid scales overlap from head to tail. Cycloid scales are circular and smooth. They are most common on fish with soft fin rays.
Ctenoid scales have a characteristic toothed edge.
They are most common on fishes with spiny fin rays. G. Body spines. Protective spines are common in slow-swimming bony fishes and bony fishes that need to protect themselves without moving. Body spines are modified scales. The spines lay flat until the pufferfish inflates its body.