Scales in Fishes

In the fishery, the skin is made up of two levels; External epidermis or epidermis and internal dermis or dermis. In fish, the lactate level plays an important part in the production of scales; hence their charges are called charcoal scales. In reptiles, birds and mammalian terrestrial creatures, the shells of the shells are derived from the superficial, so their scales are called the epidermal scales.

Scales in fish can be classified as follows:

1. Placoid scales -

Placoid scales are found in ilasmobrank fishes. The placoid scales consist of a basal plate of a circular or quadrangular shape, which is firmly attached to the skin with the help of sharpe and other connective tissues. The basal outer layer protruding from the back of the basal plate, similar to the enamel of the tooth, is made of a rigid, transparent material, vitrodentine. Beneath the vitrodentine is a level of dentine that surrounds the medulla-cavity. Blood vessels from the medulla-cavity enter the blood vessels, neural sutures and lymph vessels. There are numerous, branched microscopic tubes found in dentin, in which many long bioclasts of odontoblasts are found. The function of odontoblast cells is the formation of dentin.

2. Cosmoid scales -

This type of shark is found in extinct ostracoderm fishes. Each cosmoid shell is made up of three levels which are as follows;

a. Vitrodentine - The thin enamel-like outer layer is called vitrodentine.

B. Cosmin - A rigid, noncellular, dentin-like middle layer is called Cosmene.

C. Isopidine - Made of bone material, the internal layer with blood vessels is called isopidine.

3. Ganoid scales -

Ganoid shells are found in primitive actinopteris fishes. These scales are generally similar to tetragonal plates that join together like tiles to form external skeletons. Ganoid scales develop exclusively in chondrostian and holostean fishes. Ganoid scales are also made up of three levels, which are as follows-

a. Genoyan - The outer layer of ganoid scale is made of a hard, inorganic, enamel-like material called genoyan.

B. Cosmene - The dentin-like substance makes Cosmene the middle layer.

C. Isopidine - This level is the inner most thick and unstable.

4. Cycloid scale -

Cycloid and tenoid scales are also called Bony Ridge scales. Cycloid scales are characteristic of Teliostian fishes. These scales are thin, flexible and transparent. Because the outer and middle levels are absent in them. Cycloid scales are nearly spherical, thicker than the middle. Their center is called focus, around which concentric growth lines are located.

Cycloid scales are found in Teliost fishes, labyrinths, etc.

5. Tenoid scale -

Tenoid scales are almost like cycloid scales in shape and structure, but on their independent back are numerous, small, comb-like teeth. This type of shark is found in modern Teliost fishes like perch etc. Cycloids, tenoids and secondary types of scales can be seen on the body of some fish, such as flounders.

Variation and variation in scales -

Many variations are found in fish shells. Sharks are the transfusions of dentin present in the jaws of fish. Priestis's Sa-Teeth and Sting Ray's sting are all modified scales. In tetradon and diodon, the shells grow long and take the form of thorns. In sea horses and pipe fish, the scales are attached and make a shield of bone plates.

Use of Scales -

1. In classification and identification -

The types of shells, their configuration, number, shape and structure are different in different species of fish, which is important in identification and classification.

2. To find the number of eggs -

Androgen mark is found in some migratory fish. These fish do not take food during the overseas migration and due to lack of calcium; there is erosion of calcium from their shells. This leaves scars on calcium erosion scales, which is called the Androgen mark. Based on the number of these scars, how many times the spawn has occurred can be determined.

3. In determining age -

Growth in fish is not constant, that is, in summer, when food is abundant; the growth rate is higher than in winter. In this way, the open lines on the scales indicate the growth in summer and the tight lines show the growth in winter.