On this Wikipedia the language links are at the top of the page across from the article title. Fish come fish recipes for two many shapes and sizes. They are camouflaged as floating seaweed.
Dunkleosteus, a giant armoured arthrodire of the later Devonian. Up to 6 metres long, it lived in the Inland seas of North America. Fish used to be a class of vertebrates. There are many different kinds of fish.
They live in fresh water in lakes and rivers, and in salt water in the oceans. Some fish are less than one centimeter long. The English word “fish” does not fit neatly into cladistics, which is the scientific way to put living things into groups. So scientists call it a paraphyletic word. This means that the animals called “fish” in English do not fit into just one phylum.
Some fish are more closely related to land animals than they are to other fish. Fish” is not a formal taxonomic grouping in systematic biology. But the use of the term “fish” is so convenient that we go on using it. Fish are the oldest vertebrate group. The term includes a huge range of types, from the Middle Ordovician, about 490 million years ago, to the present day. Includes all types commonly called fish, except the lamprey.
Chondrichthyes: cartilaginous fish: sharks, rays and skates. Chondrostei: sturgeons and some other early types. Neopterygii: first seen in the later Permian, lighter and faster-moving than previous groups. Teleostei: the most successful group, Triassic to present day. They were probably a sister-group to the tetrapods.
Certain animals that have the word fish in their name are not really fish: crayfish are Crustacea, and jellyfish are Cnidaria. Some animals look like fish, but are not. Most kinds of fish have bones. Some kinds of fish, such as sharks and rays, do not have real bones. Their skeletons are made of cartilage, and so they are known as cartilaginous fish. All fish are covered with overlapping scales, and each major group of fish has its own special type of scale. These grow in concentric circles and overlap in a head to tail direction like roof tiles.
Sharks and other chondrichthyes have placoid scales made of denticles, like small versions of their teeth. The scales are usually covered with a layer of slime which improves passage through the water, and makes the fish more slippery to a predator. There are various types of eel: most are in the Anguilliformes. Their life-style has evolved many times. Eels have scales with smooth edges or are absent. There are also some important fish which breed in rivers, and spend the rest of their life in the seas. Examples are salmon, trout, the sea lamprey, and three-spined stickleback.
Fish swim by exerting force against the surrounding water. There are exceptions, but this is usually done by the fish contracting muscles on either side of its body. This starts waves of flexion which travel the length of the body from nose to tail, generally getting larger as they go along. However, there are also species which move mainly using their median and paired fins. The latter group profits from the gained manoeuvrability. This is needed, for example, when living in coral reefs.
Fish can swim slowly for many hours using red muscle fibres. They also make short, fast bursts using white muscle. The two types of muscle have a fundamentally different physiology. The red fibres are usually alongside a much greater number of white fibres. This is anaerobic metabolism, that is, it does not need oxygen. They are used for fast, short bursts.
Swimming for long periods needs oxygen for the red fibres. The oxygen supply has to be constant because these fibres only operate aerobically. They are red because they have a rich blood supply, and they contain myoglobin. Myoglobin transports the oxygen to the oxidising systems. Schools of fish can swim together for long distances, and may be chased by predators which also swim in schools. The shape of the body of a fish is important to its swimming. This is because streamlined body shapes makes the water drag less.
A smooth, rocket-shaped shark swims quickly through the water. The rocket-shape of this shark makes it an efficient swimmer. It is fast over short distances. The picture on the right shows a shark. This shark’s shape is called fusiform, and it is an ovoid shape where both ends of the fish are pointy.