The ventral side blends in with the lighter surface of the sea when viewed from below. Under ideal circumstances, neither the fish's predators nor the fish's prey can differentiate between the countershaded animal and the environment. The coloration of some fishes helps them blend in with their environment. Some fishes show disruptive coloration, a camouflage in which the color pattern of the animal contradicts the animal's body shape. In some species of bony fishes, coloration serves as advertisement to other fishes.
Some fishes rely on coloration for species recognition and sexual distinction.
Some species of fishes become brighter in color during breeding season to attract potential mates. In some species, coloration may trigger territorial behavior. He then actively defends his territory only from other fish with red bellies, notably other male sticklebacks. Coloration may change. In some species, coloration changes with age or sex change.