Fish biology: Anatomy and Physiology

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Fish biology: Anatomy and Physiology

1. Describe the structure and function of the teleost skeleton, cellular bone and the scales. Discuss the similarities and differences in function between scales and bone.

Answer:

Teleost Skeleton

Teleost is the fish group that contains the majority of the cultured fin fishes; teleost fish group is evolutionarily advanced, physically structured, contains multiple subgroups of fishes, and is the member of Teleosti infraclass. The skeleton of the teleost contains the head skull, vertebral column, and fins. The structure of these three parts of the skeleton are discussed below:

Head Skull

The structure of the head skull is suitable to provide necessary protection to eyes, brain, and other sensory organs like nose. It houses all necessary organs, like eyes, and provides shape to the face. It creates buccal cavity that supports the feeding and respiration functions. The muscles that are responsible for the movement of jaws are attached to a point created by the skull. Finally, gills’ housing is created in the form of the opercular cavity by the skull.

Vertebral Column

The vertebral column of teleost has neural spine on both sides of centrum through which the spinal cord passes. It expands throughout the body from head skull to the tail, and creates an elaborate structural frame along with the ribs. The main function of the vertebral column is to support the body from being stretched and shortened due to the contraction of the longitudinal muscles while swimming. It also helps the body cope up with the stresses to which it gets subjected when it swims fast.

Fins

Fins remain at the lower part of the skeleton. Fins are occurred in the body of the teleost in pairs and are mounted on the girdles of pelvic and pectoral areas. The posterior margin of the opercular cavity is formed by the pectoral girdle that is attached to the cleithrum bone. However, this is not the case in lower teleosts, where the pelvic girdles are not connected to the skeleton, but rather are rooted in the ventral muscle. Such structure can be found in case of salmonids. On the other hand, in the case of higher teleosts, the pelvic girdle is attached even in a delicate position, closer to anterior position, against the pectoral girdle. One such teleost is the perch.

The rays of the ventral fins and the single dorsal run the line of the haemal spines and the neural of the backbone. Both spiny and soft types of fin rays are possible. Usually, single bone spiny fins are available in the perch, whereas in case of salmonids (salmon and trout), soft fin rays are seen. In case of clupeids, such as shads, herrings and sardines, fins similar to salmonids are available.

Cellular Bone

Bones of the teleost are made of the same cellular and structural components that make the bone structure of mammalian, avian animals, and birds. The structure of the bone may be regarded as composed of an extracellular matrix, and three types of bone cells including the osteoblasts (cells that form the bone), osteocytes (the cells that reside inside the matrix), and the osteoclasts (cells that resorb bones). The growth and remodelling of the bones are controlled by the collective actions of these different cell types during the production, mineralisation, and resorption of the bone matrix. The remodelling of new bone is done instantly because of the continuous small scale operation of osteoblasts and osteoclasts cells on the surface of the bones. The bone mineralisation controlling process may essentially be seen as the mechanisms of endocrine, which performs mobilisation and deposition of phosphate and calcium. In the mineralisation of the bone, every 10 calcium molecules are attached to 6 phosphate molecules. The formula of the major calcium salts in the minerals of bone is Ca10 (PO4)6(OH)2 (chemical name Hydroxyapatite). It is thus obvious that the bone mineralisation process resorbs or deposits phosphate in proportion to calcium.

Scales

Scales create a protective layer over the skin of the teleost fish. Scales are sticky, visible, and patterned cover that keep the interior of the fish free from outside impact of the environment and help the fish maintain body temperature inside the water. Scales are calcified plates that have two sides — the outer side consists of rigged bony section and the internal side consists of fibrous connective tissue section that is partly or fully uncalcified. The scale pocket of the dermis provides the housing for scales to grow and the epidermis covers it to provide necessary protection from environmental hazards. Scales develop with the body size; the growth ring in the scales can be used as an age detector as it changes with the age of the fish. One of the major function of scales is to act as the repository of calcium that supplies additional calcium in case of high calcium demands such as during the peri