For any animal, one of its primary concerns is that it needs to survive long enough to breed and produce offspring. Fish, along with many other animals, have adopted different and intricate defense tactics 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 affect their behavior and their coloring, how they use their surroundings, and their body form. Fish can use defense in many ways, including general survival, keeping away from predators, finding and catching prey, finding a mate and breeding, and looking after their eggs and young.
Coloration
Fish come in many colors, which play a pivotal role in helping fish camouflage themselves. Not only does this help fish hide from predators, but it also allows them to prey on other fish without being seen.
Fish that are not as active generally have some camouflage coloring. Plaice, soles, angler fish, and eels have this 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 around red algae and green when found around seaweed or lettuce. 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 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 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 water’s colors.
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Schooling
Another form of defense that fishes use to avoid predators is schooling. A school of fish is several 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. Although keeping close together, the fish 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 fish.
Schooling is an excellent defense method, but it does come with its constraints. All the fish must be of the same swimming capability and about the same size. Different-sized fish do form 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 correctly, they won’t move with the rest of the school and may be picked off by a predator.
Staying Alone
Schooling is an excellent means of defense for fish, especially for small fish. However, swimming on their own is also a reasonable means of protection. Solo fish swimming has to keep hidden and remain out of sight. A low profile is adopted to survive any predators.
Much 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. They can keep themselves safe from predators by exploring small habitats, such as coral, sponges, and rock crevices.
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Senses
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 reasons, including sight and sound.
Schooling fishes rely on sight and sound to keep together, moving like one large fish. The company plays a large part in this as the fish constantly look at each other to maintain the school’s cohesion. However, blind fish swim in schools, and their senses come from changes in pressure from the other members and the shift in direction in the water.
Sound also plays a part in the schooling fish, as the 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 detects vibrations and movement in the water around them. It is a system of tactile sense organs in the head and on both sides of the body. It is used to detect movement and vibration in the surrounding water.
Venom
There are several fish that use a mixture of toxins called venom. They deliver 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 young can die from stinging. For most of us, 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 fatal sting.
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Spines
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 bellies, making them unattractive to predators.
Fish that have spines often grow them during the early larval stages. This stops the young from being eaten by predators, even if they are too young to protect themselves.
Panic
The most prominent family of fish in North America is the minnow, which produces a substance that can cause panic in the fish around them.
Coming from some cells in the skin, the minnow can produce a substance that causes panic in the rest of the school. This substance also seems to be released when a minnow is 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.
Releasing this when an animal is injured or dies is a great defense mechanism for other fish. If one fish dies, the rest of the school knows the danger and will react accordingly.
Carp uses this mechanism to live in freshwater, where visibility is unsuitable due to plants and mud.
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Bryan Harding is a member of the American Society of Mammalogists and a member of the American Birding Association. Bryan is especially fond of mammals and has studied and worked with them around the world. Bryan serves as owner, writer, and publisher of North American Nature.