Barbels Whisker-like feelers near the mouths of bony fish, rays and some sharks. They contain taste sensors that help fish to find food in dark or murky water.

Blowfish A medium-sized fish that can inflate its body to more than twice its size by swallowing water. This causes sharp, poisonous spines to stick out all over its body, scaring off any predators. It is also sometimes called a porcupinefish.

Bony fish A group of fish with skeletons made of bone. Their bodies are mostly covered with overlapping scales and they usually have swim bladders to keep them afloat.

Cartilaginous fish A group of fish including sharks and rays whose skeletons contain no bone—only a flexible, fibrous material called cartilage. Cartilaginous fish also have no swim bladder organs to help them to stay afloat. They must therefore swim continuously to stop themselves from sinking to the bottom of the ocean.

Caudal fin The tail fin of a fish used to move it through the water.

Dorsal fin A fin on the back side of fish, sharks and marine mammals like whales and dolphins. It helps keep the animal upright while swimming.

Eel A long, ribbon or snake-like fish without scales. Eels have long bodies with narrow dorsal fins that do not stick out from their bodies like other fish. They live in the world’s oceans and rivers. Their young are called elvers.

Fins The broad, flat surfaces projecting from the body of marine animals such as fish. They are used for steering and balance.

Flatfish A group of bottom-living fish, including flounder, plaice, halibut, turbot 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 ocean floor.

Flyingfish A fish with large pectoral fins like wings. These allow the flyingfish to swim fast and leap from the water to escape from predators.

Gills The breathing organs of fish, which extract oxygen from the water. Fish draw water, which contains oxygen, into their mouths. When they pump it out through slits in the side of their head, it passes over the gills and tiny blood vessels extract the oxygen. Bony fish usually have a protective flap over their gills, called the operculum.

Jawless fish Long, tube-like fish that have no jaws. They have existed for around 520 million years, but the lamprey and hagfish are the only species still alive today.

Lionfish A striped, tropical fish, armed with venomous spines on its back. The lionfish's bright markings warn other animals that it is poisonous.

Pectoral fin The fin located on each side of a fish’s body, used to help the fish steer.

Scales Tiny, layered plates that cover the bodies of many bony fish. Most fish have scales that overlap each other to keep water out and to protect the fish’s body.

School A group of fish or marine mammals, such as dolphins, swimming as a group in the same direction.

Shoal A number of fish that stay together as a social group. Shoaling means that fish have a better chance of survival if they are attacked by predators, and a better chance of finding a mate.

Stonefish A mottled red fish with venomous spines down its back. The stonefish lives on the seabed in tropical waters, where it is perfectly camouflaged. Its spines stick up when it is threatened and can inject a venom that is fatal even to humans.

Swim bladder An internal organ filled with air that helps bony fish stay at a certain depth. Swim bladders enable bony fish to stay buoyant without needing to swim. They also help bony fish sense sound vibrations in the surrounding water.

Swordfish A large predatory fish with a distinctive long, flat, sword-like snout. Swordfish have long, streamlined bodies up to 4.5 metres (14.75 feet) long. They hunt at night near the ocean surface, using their snouts to stun prey before eating it. They swim at great speed, sometimes leaping out of the water and briefly travelling through the air at speeds of up to 120 km/h (75 mph).

Vertebrates Animals with a backbone. Fish are the largest and most diverse group of vertebrates.

Consultant: Chris Jarvis