How Do Fish Defend Themselves?

For any animal, one of its primary concerns it needs to be able to survive long enough to breed and produce offspring. Fish, along with many other animals have adopted many different and intricate defense tactics that they use to survive.

Fish defend themselves using a variety of techniques. They use their color to camouflage themselves from predators. Many fish also form a school of hundreds or thousands of small fish to protect themselves. Fish use their five senses and some have spines or venom.

The defense tactics they use not only affect their behavior but also their coloring, how they use their surroundings, and their body form. The defense can be used by the fishes in many ways, including general survival, keeping away from predators, being able to find and catch prey, finding a mate and breeding, and looking after their eggs and young.


Fish come in many colors and these different colors play a pivotal role in helping fish camouflage themselves. Not only does this help fish hide from predators, but also allows it to prey on other fish without being seen.

Fish that are not as active generally have some sort of camouflage coloring. Plaice, sole, angler fish, and eels have this sort of coloring. Some fishes such as the Arctic shanny can change their colors to match the habitat around them. The Arctic shanny has been seen to take on red coloring when around red algae, green when found around seaweed or lettuce or brown. The food that these fish feed on can also change their color.

When we look at some pictures of colored fish we may wonder how they can be camouflaged when in the water, but these colors can help them.

Fish with greeny-brown or blue backs with silver undersides is excellent concealment when in open water. Fish such as herring and mackerel are some of the fish that benefit from these colorings when in the water.

From below, the silvery underparts and sides of the fish can not be seen against the reflections from the surface of the water above. When looked at from above, the dark brown or blue colors blend with the colors of the water.


Another form of defense that fishes use to avoid predators is schooling. A school of fish is a number of fish that swim together. Schools of fish can be huge with several thousand fish.

Predators that come across a school of fish can be confused by the sheer number of fish. The fish, although keeping close together do not move as one, and the predator can have trouble picking out one fish, as that fish is replaced in the school by another and another fish.

Schooling is a great defense method, but it does come with its constraints. All the fish in the school must be of the same swimming capability and must all be about the same size. Different sized fish do form their own schools, but outsized fish may have trouble moving in a school.

Another problem with schooling is for any fish that are disabled or have eye problems or parasites. If the fish cannot see properly then they won’t be able to move with the rest of the school and maybe picked off by a predator.

Staying Alone

Schooling is a great means of defense for fish, especially small fish. However, swimming on their own is also a good means of defense. Solo fish swimming have to keep hidden and remain out of sight. A low profile is adopted in order to survive any predators.

Many solitary fish live in vegetation or under stones during the day, only coming out at night to feed. Solitary fish are also well camouflaged in their coloring.

Small fish have an advantage over large fish when swimming on their own. By exploring small habitats, such as coral, sponges and rock crevices they can keep themselves safe from predators.


Whether solitary or in schools, camouflaged or not, all fish rely on their senses to survive against being eaten by another predator. Fish have excellent senses including sight and sound.

Schooling fishes rely on sight and sound to keep together, moving as if one large fish. Sight plays a large part in this as the fish are constantly looking at each other to keep the school’s cohesion. However, blind fish also swim in schools, and their senses come from changes in pressure from the other members and also the change in direction in the water.

Sound also plays a part in the schooling fishes, as the sound of a school makes a noise in the water. Fish hear this noise and can swim accordingly.

Fish also have a series of sense organs in the head and along both sides of their body. This lateral line system is used to detect both vibrations and movement in the water around them It is a system of tactile sense organs located in the head and along both sides of the body. It is used to detect movement and vibration in the surrounding water.


There are several fish that use a mixture of toxins called venom. They deliver the venom by biting, stinging or stabbing their prey.

The lionfish can be found throughout Florida and even up into North Carolina. They are about 12 to 15 inches and deliver venom through their dorsal and pectoral fins.

Although not deadly to most people, the elderly or very young can die by being stung. For most of us, the venom can cause vomiting, fever, convulsions, nausea and dizziness.

For other fish though, the venom from a lionfish can be deadly. Lionfish also use their coloration of red and white bands to let predators know that they can deliver a deadly sting.


Some fish have another, more visual defense mechanism on their body. They use spines around the body and fins to ward off predators. Fish such as the stickleback have long spines along their backs and on their bellies which make them unattractive to predators.

Fish that have spines often grow them during the early larval stages. This stops the young being eaten by predators even if they are too young to protect themselves.


The largest family of fishes in North America is the minnow and these produce a substance that can cause panic in the fish around them.

Coming from some cells in the skin, the minnow can produce a substance which causes panic in the rest of the school. This substance also seems to be released when a minnow as killed as this also causes panic in other minnows.

It is not just minnows that release this substance. Carp and perch also release this substance, however this substance only affects members of the same species.

By releasing this when an animal is injured or dies, this acts as a great defense mechanism to other fish around. If one fish dies, then the rest of the school know that there is danger around and will react accordingly.

Carp use this mechanism as they live in fresh water where visibility is not good due to the amount of plants and mud.

Bryan Harding

Bryan has spent his whole life around animals. While loving all animals, Bryan is especially fond of mammals and has studied and worked with them around the world. Not only does Bryan share his knowledge and experience with our readers, but he also serves as owner, editor, and publisher of North American Mammals.

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