Anatomy of fishes
Fish anatomy refers to the structure of the body and organs of fish and the field of biology that studies this anatomy of fish. The body structure of fish has been shaped as a result of evolution to meet the demands of their aquatic environment. Other vertebrates have evolved from primitive fish, and the diversity of fish and their structure is older than that of terrestrial vertebrates.
Almost all fish belong to thermostable vertebrates. Thus, the spine and the associated skull act as the supporting framework for the fish's body. The largest group of fish, the bony fishes, have a bony backbone and the rest of the supporting structure associated with it, but the backbone of cartilaginous fish (sharks, rays and kingfishers) and ringmouths (echinoderms) is almost entirely made of cartilage, and ringmouths also lack jaws.
Since fish are perfectly adapted to aquatic life, their body is usually very streamlined, which makes swimming easier. Fish use their entire body to move effectively, but the actual locomotor organs are the fish's fins. With them, the fish maintains its balance and guides its swimming. In addition, the fish can regulate its swimming depth with the help of a gas-containing swim bladder located in the fish's body cavity.
Despite everything, different fish species can be very different in size and appearance. Often a lot can be directly deduced from the appearance of the fish's living conditions. The side-flattened shuttle shape is generally considered the basic shape of a fish, but there are also many different shapes, because the shape of the fish's body has always adapted to its habitat. For example, fish that live at the bottom of water bodies are often flattened, round or flexible and snake-like in shape. On the other hand, fish that live close to the surface are nimble because they have to be able to move quickly. The body of a fish can be roughly divided into the head, middle body and tail, although the parts are not clearly demarcated. In most species, the caudal edge of the gill cover serves as the border between the head and the midbody. The caudal shaft of a fish is the narrow part of its body at the caudal end. The number of vertebrae varies greatly among different groups of fish. Usually, the two-part dorsal fork of the vertebrae is fused together at the tip, and the spinal cord runs in the small space between the forks. At the trunk vertebrae, the lateral abdominal branches support the ribs. The lower ends of the ribs are free, which is due to the absence of the sternum. Fish bones are mainly flexible rods that move at the base.
The skin of fish protects their internal organs from bumps and also forms a mechanical barrier against diseases. Most fish species have a layer of scales covering the skin. Scales are flat structures formed as a result of the ossification of the dermis, which attach to the scale pockets of the deepest skin layer and cover the topmost skin layer. There are color cells in the top skin layer that can adjust the amount of color. Some fish have even developed the ability to change their color according to the background color of the environment. The mucus covering the skin protects the fish from the penetration of microorganisms through the skin into the body. As the fish ages, the bones grow as well as the scales, which can be used to determine the age of the fish on the basis of the annual rings that form on them. Age can also be estimated using the annual rings of the gill cover in those species that have a gill cover. Roundmouths do not have scales on their skin, and the scales of cartilaginous and sturgeon fish, for example, are quite different from those of developed bony fish.
On the head of the fish is its snout, which refers to the part of the head extending from the eyes to the front end of the upper jaw, the lower jaw, the gill covers (missing in sharks) and the cheeks. Both the muzzle, gill covers and cheekbones can have protruding spines. The fish has teeth in the jawbones and mandible, but teeth are missing in the upper jaw