Musculoskeletal system of fish

The skeleton and muscles are part of the musculoskeletal system.

The skeleton provides support for the body and organs of movement, protects the most important organs.
Due to the work of the muscles, movement is carried out.

The skeleton is divided into 4 sections:
skeleton of the head (skull);
trunk skeleton;
the skeleton of the girdles of the limbs;
the skeleton of the fins.

Head and torso skeleton

The backbone and skull form the basis of the internal skeleton of a fish.

The spine of a fish consists of a large number of vertebrae. It distinguishes between the trunk and tail sections.

The trunk vertebrae have a body, superior and inferior arches. The upper arches, following each other, form a channel in which the spinal cord is located. The lower arcs grow laterally in the form of two transverse processes. Ribs are usually attached to them.

The upper and lower arches of the caudal vertebrae have the same structure. The lower arches of the vertebrae form a canal in which blood vessels pass.

In front, the spine is motionlessly connected to the skull, which consists of the cerebral box and bones that form the jaw, the bones of the eye sockets and the branchial apparatus (gill arches and gill covers).
Some bones (highlighted in brown and yellow) are part of the skeleton of the pectoral girdle of the limbs.

The gill arches can be seen under the large gill covers, if they are raised. The branchial arches constitute the skeleton of the respiratory apparatus, that is, they serve as a support. There are gills on them.

Skeletons of unpaired and paired fins

The skeleton of unpaired fins consists of many elongated bones, reinforced in the thickness of the musculature.

The paired fin skeleton consists of a girdle skeleton and a free limb skeleton.

The skeleton of the pectoral girdle is attached to the skeleton of the head (bones highlighted in brown and yellow).

The skeleton of the free limb (the fin itself) includes many small and elongated bones.

The abdominal girdle is formed by one bone.

The skeleton of the free pelvic fin is composed of many long bones.

The main muscles are distributed evenly in the dorsal part of the fish’s body; the muscles that move the tail are especially well developed.

The swim bladder is a special organ found in almost all teleost fish and develops as an outgrowth of the esophagus. It helps the fish stay at a certain depth, where the weight of the water displaced by the fish is equal to the weight of the fish itself. When the fish sinks below this level, its body, experiencing greater external pressure from the water, contracts, squeezing the swim bladder. In this case, the weight of the displaced volume of water decreases and becomes less than the weight of the fish and the fish begins to fall down. The lower it falls, the stronger the water pressure becomes, the more the fish’s body is compressed and the more rapidly its fall continues. On the contrary, when surfacing closer to the surface, the gas in the swim bladder expands and reduces the specific gravity of the fish, which pushes the fish even more towards the surface.

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