How do Fish Defend Themselves From Predators?

14 April 1998

Fish have an amazing assortment of defenses. Most fish hide or use camouflage to protect themselves. But others use a variety of defenses such as protective spines, electric shock, chemicals and even venom for protection from predators.

Camouflage creates deceptive appearances and helps animals avoid detection. Probably the most widely used form of camouflage among fish is countershading. Most fish have dark backs and white bellies. The dark back helps them blend in with the dark bottom or depths when viewed from above, whereas the white belly helps them blend with the sky when viewed from below.

Many fish are colored to match their backgrounds and, therefore, appear invisible. This feature is particularly important for sluggish bottomfish. Some species are capable of changing their color to match their background, a process called cryptic coloration. The master of this process is the flounder, which can quickly change its color pattern to match the bottom on which they are resting. In the lab, some individuals have even produced a fair approximation of a checkerboard when placed in an aquarium with that pattern on the bottom.

Another form of camouflage is colors and patterns that break up the outline of fish, making them harder to see. One of the most common patterns of this type is vertical bars running down each side; this pattern is associated with fish that live near beds of aquatic plants. The vertical bars on the fish blend in with the vertical pattern of the plant stems making the fish difficult to see. Lateral bands, single dark bands running along the side of a fish, are most often seen in schooling fish. They may help confuse predators because the bands tend to blend together making it difficult for the predator to single out one individual.

The eyes of a fish are perhaps its most visible feature and frequently the focus of attacks by predators. One of the most common marks on fish, especially juvenile fish, is a black spot located near the base of the tail. The spot, about the size of an eye, serves to confuse predators. The attacker aims for the tail rather than the head, giving the victim a greater chance to escape.

Instead of relying on camouflage and confusing markings, some fish are more offensive in their defense. Poison is one of the defenses developed by a number of sea creatures. It may be administered by teeth, spines, or barbs. The scorpionfish, marine and freshwater catfish, and toadfish are just a few species of fish that have sacs of poison at the base of their spines. If a predator threatens the scorpionfish, it first displays its brightly colored fins as a warning. If attacked, the scorpionfish moves to pierce the attacker with its spines and inject it with venom.

Some fish, such as the electric eel and the torpedo ray, even have electrical properties they use for protection. These fish can deliver powerful electric shocks through the water which stun their predators and allow the potential victim time to escape.

Special chemicals are used by some fish species to warn others in their group of danger. Minnows release a substance into the water when they are attacked; other minnows respond to the chemical by swimming away. Still other fish release deadly chemicals into the water. The Moses sole, a flounder from the Red Sea, releases milky poison so powerful that even sharks are repelled.

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