The body of a fish is nervous system connection point diagram pdf into a head, trunk and tail, although the divisions between the three are not always externally visible. They are supported by the muscles which compose the main part of the trunk.
The eyes are adapted for seeing underwater and have only local vision. Their bodies tend to be dorso-ventrally flattened, they usually have five pairs of gill slits and a large mouth set on the underside of the head. Bony fish have a swim bladder which helps them maintain a constant depth in the water column, but not a cloaca. At the broadest level their body is divided into head, trunk, and tail, although the divisions are not always externally visible. They are supported only by the muscles. The ribs attach to the spine. Fish bones have been used to bioremediate lead from contaminated soil.
The vertebral arch surrounds the spinal cord, and is of broadly similar form to that found in most other vertebrates. Both of these structures are embedded within a single cylindrical mass of cartilage. The upper tube is formed from the vertebral arches, but also includes additional cartilagenous structures filling in the gaps between the vertebrae, and so enclosing the spinal cord in an essentially continuous sheath. Even the arches are discontinuous, consisting of separate pieces of arch-shaped cartilage around the spinal cord in most parts of the body, changing to long strips of cartilage above and below in the tail region. Others consider them a sister group of vertebrates in the common taxon of Craniata. The operculum and preopercle may or may not have spines. In most jawed fish, however, there are three general configurations.
The jaws consist of separate hoops of cartilage, almost always distinct from the cranium proper. The roof of the skull is generally well formed, and although the exact relationship of its bones to those of tetrapods is unclear, they are usually given similar names for convenience. Many fish species also have a variety of protrusions or spines on the head. It is thought that the original selective advantage garnered by the jaw was not related to feeding, but to increased respiration efficiency. 3-D expansion of the buccal cavity.
Others have no outer covering on the skin. There are four principal types of fish scales. They are distinguished by spines that cover one edge. In most species, it consists of a line of receptors running along each side of the fish. Their principal function is to help the fish swim. Fins located in different places on the fish serve different purposes, such as moving forward, turning, and keeping an upright position.
For every fin, there are a number of fish species in which this particular fin has been lost during evolution. In bony fish, most fins may have spines or rays. A fin may contain only spiny rays, only soft rays, or a combination of both. Spines are generally stiff, sharp and unsegmented. Rays are generally soft, flexible, segmented, and may be branched.
Spines have a variety of uses. They are actually segmented and appear as a series of disks stacked one on top of another. Most fishes have one dorsal fin, but some fishes have two or three . The dorsal fins serve to protect the fish against rolling, and assists in sudden turns and stops. There are two to three of them: “proximal”, “middle”, and “distal”. In spinous fins the distal is often fused to the middle, or not present at all.