Coral reef fish

Coral reefs are found in shallow waters around coastlines in warm, tropical seas. The reef waters teem with a wide variety of brightly coloured fish. Many of the smaller kinds feed on tiny plants, called algae, inside the coral. Predators, such as sharks, rays and barracudas, prey on coral reef fish. To defend themselves, many coral reef fish have sharp, bony spines in their fins.

There are many kinds of coral reef fish. They include angelfish, butterflyfish, parrotfish, triggerfish, zebrafish and lionfish. The clownfish is a small orange and white fish. It lives inside the poisonous tentacles of sea anemones. The fish is protected from the poison, but its enemies would be stung to death. In return for its protection, the clownfish keeps the anemone clean.

Fish that live in deep waters all the time must cope with the extreme cold, total darkness, high pressure and the scarcity of food. Deep-ocean fish have special light-producing organs and large eyes to see in the near-blackness. Prey comes along only rarely. To take advantage of any prey that does come their way, predators have huge jaws, long fangs and stretchy stomachs. Among kinds of deep-ocean fish are viperfish, anglerfish, gulper eels and hatchetfish.

Eels

Eels are snake-like fish. Their long, thin bodies are smooth. They do not have scales. There are around 800 kinds of eel. They live in both oceans and rivers. Some are just a few centimetres in length, while the conger and moray eels can grow to 3 metres (10 ft) long. Eels swim by making their bodies wave from side to side. Their young are called elvers.

European eels grow up in freshwater streams across Europe. When they are about six years old, they travel more than 6000 kilometres (3700 miles) out across the Atlantic Ocean. They lay their eggs in the warm, still waters of the Sargasso Sea. Their young then drift back in ocean currents all the way to Europe.

Flatfish

Flatfish are a group of bottom-living fish. They include the flounder, halibut, plaice and sole. They have both eyes on one side of their flat bodies, so that they can spot predators or prey above them in the water. They are camouflaged to blend in with the sandy bed of the shallow seas where they live.

Flying fish

Flying fish leap into the air to avoid predators. They use their large, wing-like fins to glide over the surface of the water. A flying fish can cover up to 90 metres (300 feet) in one “flight”. However, when they are in the air they can be more easily seized by birds.

Forage fish

Forage fish are small fish preyed on by larger predators: big fish (including the tuna, sailfish and sharks), seabirds and marine mammals. The forage fish themselves feed on plankton. They form large groups, sometimes containing thousands, or even millions, of fish, called shoals. Herrings, sardines, shad, anchovies, capelin, fusiliers and sprats are all forage fish.

Lampreys and hagfish

Lampreys and hagfish look like prehistoric fish that lived more than 300 million years ago. Both have eel-like bodies and skeletons made of cartilage. Neither has jaws. Instead, they have rows of short, sharp teeth which they use to bore into the flesh of other fish.

Lionfish

The colourful striped body of the zebra lionfish warns its enemies that its spines are venomous. They are deadly to touch, with each fin containing enough venom to kill its prey. Lionfish sometimes blow jets of water at their prey. This confuses it, making it more easily snapped up by the lionfish.

Ocean sunfish

The ocean sunfish, or mola mola, is the world's heaviest bony fish. It lives in tropical or temperate waters. Measuring about 1.8 metres (6 feet) long, it weighs up to 1050 kilograms (2300 pounds). It has a huge, round, flattened body. On account of its large fins, it can be as tall as it is long. Using its fins as oars to pull itself through the water, the ocean sunfish feeds mainly on jellyfish. It is so-called after its habit of lying on its side basking in the sun at the water's surface.

Porcupinefish

Sometimes called the blowfish, the porcupinefish has its own, special way of defending itself. When threatened, it puffs itself up into a balloon shape. Its sharp spines stick out in all directions. The porcupinefish is poisonous if eaten.

Rays and skates have soft skeletons made of cartilage. They have flat bodies and long tails. Most live on the sea floor in coastal waters. Both their gills and mouths are on the undersides of their bodies. To swim, they flap their wing-like fins. It looks as if they are flying through the water. They feed on fish and shellfish near the seabed. They use their rounded teeth for crushing shells. Rays give birth to live young, while skates lay eggs.

The stingray has a spine in its tail. It uses it to inject a painful venom into any predator that tries to attack it. The stingray lives on the sea bed in shallow, tropical waters. The electric ray stuns its prey by giving it an electric shock.

Salmon is the name for the family of fish that includes both salmon and trout. Most salmon hatch out in freshwater streams. The young fish, called parr, grow up there, before swimming downriver and out into the ocean. Years later, they return to the same stream where they were born to lay their eggs. It is a long and exhausting journey. They have to battle against strong currents and waterfalls. Along their journey, some kinds of salmon change colour, from silvery-blue to bright red.

Seahorses

Seahorses are very strange-looking fish. They swim slowly through shallow waters in an upright position. In fast-moving water, they hang on to sea plants with their long tails. Seahorses probably mate with a single partner for life.

Seahorses have an unusual way of giving birth. The female puts her eggs into a pouch on the male’s body. There they develop until one day the male “gives birth” to 50 or more baby seahorses.

Sharks have skeletons made of soft cartilage (gristle), rather than bone. They are mostly predators, although the largest kinds of all, the whale shark and basking shark, feed only on plankton. To hunt their prey, sharks rely on their sense of smell and their ability to detect movement in the water. Many sharks have large, razor-sharp teeth set in rows.

Stonefish

The stonefish is one of the deadliest fish in the world. Lying in wait on the sea bed, perfectly camouflaged among the stones, it injects poison into anything that touches it. It can injure or even kill any person unlucky enough to step on it.

Predators of the warm oceans, tuna are some of the fastest-swimming fish of all. The yellowfin tuna can swim at speeds of up to 75 km/h (47 mph). Tuna is a popular catch for fishing boats. As a result of overfishing, stocks of some kinds of tuna are close to extinction.