Fish are animals that live in water. They are vertebrates, animals with backbones, and come in all kinds of shapes, sizes and colors. Fish first appeared in the oceans of the Earth about 500 million years ago, long before dinosaurs roamed our planet. Today there are tens of thousands of different kinds of fish and new species are discovered every year. Over millions of years fish have changed their features and adapted to their surroundings in order to survive.
The whale shark is the largest fish on Earth. It can grow up to 12 meters in length and can weigh up to 15 tons. In contrast tiny gobies are often only a few mm long.
Fish are important to people. They were among the first animals hunted by primitive human beings. Millions of people all over the world depend on fish as a main form of nutrition. In many coastal countries, for example Japan or Norway, people depend on fishing to make a living.
Fish are a part of the food chain. They eat animals and are eaten by other sea creatures, thus keeping up the balance of nature.
Where fish live
Fish live all over the world, in the cold water of the Arctic as well as in warm tropical water around the equator. Areas rich in fish are especially around the coastal shelves of the Northern Atlantic, the Caribbean Sea and the western Pacific Ocean.
Most of the world’s fish live in salt water. They preferably live in areas where warm and cold currents meet. Some types live in the warm tropical waters around coral reefs.
About 40% of all fish species are in fresh water. They include carp, catfish, trout or bass. Some of them live in the clear water of rivers while others prefer muddy pond water. A few types of fish can swim in both salt and fresh water. Salmon, for example, are born in fresh water , migrate to the ocean and then return to fresh water to reproduce.
The sea dragon is close relative of the sea horse
Bodies of fish
Fish have no neck. The head and body are combined to one. Most species have a skeleton made of bone, only a few species have backbones made of cartilage.
Most fish are shaped like cigars or torpedoes, so that they can travel very quickly. Fish that swim near the ocean floor are flat-shaped. Eels look like long snakes under water.
Fish are cold-blooded. Their body temperature changes with their surroundings. Almost all fish have fins, instead of arms and legs, which they use for swimming.
The skin of most fish is made out of a special slippery substance. It is covered by small plates called scales. Some scales have special cells that give fish a certain color.
Fish breathe oxygen from the water they live in. Gills on the side of a fish’s head absorb oxygen from the water and release carbon dioxide into it.
Some animals in the oceans of the world look like fish but are actually mammals. Dolphins and whales have lungs and must come up to the surface for air.
Fish have organs that tell them what is happening in the water around them. They can see left and right at the same time. Although they have no physical ears they have hearing organs on the side of their head. They not only can hear sounds in the water but can also sense sounds that happen on the surface.
All fish have a sense of smell. In some species, for example sharks and salmon, it is highly developed. Fish can also feel pressure of water movements, thus feeling dangers that approach them.
Fish have a special sense called the lateral line. It is a row of cells that works like radar and help them navigate through waters.
How fish live
Most fish eat meat, preferably other fish. They also eat plants, worms and algae. The largest fish in the world consume huge masses of plankton.
Fish have to protect themselves from being eaten by other fish. They blend into their surroundings by changing their color or their shape. Some fish are very fast swimmers and get away from their enemies very quickly. Others release poisonous substances from their spines.
Although most fish are harmless to humans some will attack if provoked. Sharks attack humans if they smell blood or if people make uncontrolled movements. Piranhas live in the waters of the tropical rainforest. They attack their victims with their sharp teeth and tear their flesh apart.
The whale shark is the world's largest fish
How fish reproduce
Fish reproduce by releasing male sperm and female eggs into the water at the same time. The process of joining together is called spawning. Eggs are food for other fish. Many females release hundreds of thousands of eggs to make sure that at least some of the young ones can survive.
Many fish leave their eggs after spawning. Some of them stay and protect their eggs until they hatch. Salmon cover their eggs with sand and gravel.
Danger to fish
Fish are caught for a number of reasons. Apart from providing food for millions of people they are used for animal feed and to produce oil.
Overfishing in the world’s oceans poses a threat to many species. Some are in danger of dying out. Catch quotas have been introduced to save some of the most important species. Fish are also endangered by pollution of the world’s oceans.
- Animal Migration
- Corals and Coral Reefs
- Marine Biology - Life Forms and Habitats in the World's Oceans
- Increasing Jellyfish Population May Lead to Environmental Disaster
- Fukushima's Effects on the World's Oceans
- Great White Sharks in the Mediterranean Sea Came from Australia
- Scientists Discover Plankton Under the Ice of the Arctic Ocean
- absorb = take in
- adapt = to change and get used to a new situation
- algae = very simple plant without leaves that grows in or near water
- although = while
- appear = here: exist
- approach = to come towards something
- area = place
- attack = use violence to hurt someone
- backbone = a row of connected bones that go down the middle of your back
- carbon dioxide = gas that animals breathe out
- cartilage = strong substance that can bend; it is around the moveable parts of your body
- catfish = fish that has whiskers around its mouth and lives in rivers and lakes
- coastal = in the sea near the coast
- coastal shelf = edge of a continent where it slopes down steeply to the bottom of the sea
- combine = unite, join
- consume= eat
- creature = living thing
- current = movement of water in the ocean
- depend on = need
- discover = to find for the first time
- eel = long thin fish that looks like a snake
- especially = above all
- fin = thin body part that a fish uses to swim
- flesh = soft part of a person or animal that is between the skin and the bones
- food chain = a plant or animal is eaten by another plant or animal; this goes on over and over again
- gill = organ on the side of a fish through which it breathes
- harmless = not dangerous
- highly developed = very good
- human being = person
- in contrast = on the other side, in comparison
- include = consist of
- length = how long something is
- mammal = type of animal that drinks milk from its mother when it is young
- migrate = move, travel
- movement = the way something moves
- muddy = dull, not clear
- navigate = to find your way around
- nutrition = food
- oxygen = gas that has no color or smell and that is in the air that we breathe
- physical = bodily ; an organ you can touch
- plankton = very small forms of plant and animal life that live in water and are eaten by fish
- plate = thin piece used as a cover
- poisonous = deadly
- preferably = if possible
- pressure = weight, force
- protect = defend
- provoke = to make angry
- radar = machine that uses radio waves to find the position of things
- release = set free
- reproduce = lay eggs that young fish come out of
- roam = wander around
- row = line
- salmon = large fish with silver skin that lives in the sea but swims up rivers to lay its eggs
- scale = small flat piece of skin
- sense = to feel that something exists
- shape = form
- skeleton = structure of bones
- slippery = oily, greasy
- species = group of plant or animals whose members are almost the same and can have babies together
- spine = row of bones down the center of your back
- substance = material
- surface = top layer of something
- surroundings = the world around you
- survive = to live on after a dangerous situation
- thus = therefore
- trout = common river fish that can be eaten
- vertebrate = a living creature that has a backbone
- weigh = how heavy something is