And in the dark ocean depths are weird fish like the deep-sea angler, which gets its name from the glowing bulb it dangles in front of its mouth to attract prey, like bait on an angler's rod. Plaice spend nearly all their life lying on their side on the sea-bed. Halibut and other flatfish have both eyes on the same side of their bodies. Mackerel are related to tuna and are some of the fastest swimmers in the sea. Tuna grow up to 700kg and are very important food fish, caught widely for canning.
Herring often live in huge shoals, millions strong, especially in the Atlantic and Indian oceans.
Swordfish and marlin are big fish that live near the surface of the open ocean. Conger eels are long, snake-like fish that haunt crevices in rocky reefs and wrecks. Moray eels are among the most common of all eels. They are fearsome predators that grow up to 3m long and feed on small fish and shrimps. Coelacanths are often described as living fossils, and were once thought to have been extinct for 70 million years.