One of the most striking features of fish is their colorization. Coloring and body marks on fish help them avoid predators by staying out of sight. Many prey species, such as gulf flounder, avoid being eaten by blending in with their surroundings, matching the subtle shades of their habitats. Spotted fish look like the seafloor, and striped fish blend in with grasses. Some reef fish display bright colors because they live among brightly colored sponges and corals.

Sand gulf flounder
Sand gulf flounder

Conversely, coloring that mimics fish’s habitats helps predators get close to their prey. The ability to avoid detection is a significant advantage for such hunters as scorpion fish that wait quietly until prey comes within striking distance. A hunter is able to conserve both time and energy if it does not have to pursue its food. Most fish, including sea trout and grouper, display some degree of countershading.

This form of coloring reduces the clarity of the fish’s body outline in water. The simplest, and most common, form of countershading is a dark dorsal side and a pale ventral side, with intermediate colors between the two. When sunlight filters down through the water, it lightens the fish’s back and throws shadows on its underside. The overall effect of countershading lessens the degree of contrast between the fish and the water.

A few species of fish, such as the spotfin butterfly fish and the high hat fish, show disruptive or deflective colorization that includes bands, stripes, or dots of contrasting colors. These colors and patterns confuse predators by distorting the true shape, size, and position of the fish. Bright patterns draw the predator’s eye, causing it to see the pattern rather than the fish itself. This type of coloring can deflect the predator’s attention away from a fish’s vulnerable areas, such as its head and eyes.

Colorization can also be used as an advertisement. There is no point in being poisonous and unpalatable if no one knows it. Instead of hiding, poisonous fish announce their dangerous status. Fish may also advertise their age or sex with coloring. Males are generally more colorful than females, whose duller shades help camouflage and protect them. Young fish may be transparent or pale, making it hard for predators to spot them, as well as letting the older fish of their own species know that they are not a threat.