Who is the most famous aquatic creature? Of course, fish. But without the scales, her life in the water would be almost impossible. Why? Find out from our article.
Why do fish need scales
Integuments of the body are of great importance in the life of fish. Like iron chain mail, they protect the skin and internal organs from friction and water pressure, the penetration of pathogens and parasites. The scales give the fish a streamlined body shape. And for some species, it is a reliable shield against the teeth of the enemy.
There are practically no fish without scales. In some species, it covers the entire body from the head to the dorsal fin, in others it stretches parallel to the spine in separate stripes. If the scales are not visible at all, this means that it is reduced. It develops in the dermis, or corium of the skin, in the form of bone formations. This forms a dense protective cover. Examples of such fish are catfish, burbot, snake fishermen, sterlet, sturgeon and lamprey.
Chemical composition
Fish scales are bone or cartilaginous derivatives of the skin. Half of its chemical elements are inorganic substances. These include mineral s alts, namely phosphates and carbonates of alkaline earthmetals. The remaining 50% are organic substances represented by connective tissue.
Types of fish scales
Fulfilling the same functions, leather derivatives differ in their origin and chemical composition. Depending on this, several types of scales are distinguished. In representatives of the class Cartilaginous, it is placoid. This species is the most ancient in its origin. The skin of ray-finned fish is covered with ganoid scales. In bone, it looks like scales that overlap one another.
Placoid scales
This type of fish scale has been found in fossil species. Among modern species, its owners are rays and sharks. These are diamond-shaped scales with a clearly visible spike that protrudes outward. Inside each such unit is a cavity. It is filled with connective tissue, permeated with blood vessels and neurons.
Placoid scales are very strong. In stingrays, it even turns into spines. It's all about its chemical composition, the basis of which is dentin. This substance is the basis of the plate. Outside, each scale is covered with a vitreous layer - vitrodentin. Such a plate is similar to the teeth of fish.
Ganoid and bone scales
Ciste-finned fish are covered with ganoid scales. It is also located on the tail of sturgeons. These are thick rhombic plates. Such fish scales are interconnected with the help of special joints. Their combination can be a solid shell, scutes or bones on the skin. On her bodyarranged in rings.
This type of scale got its name from the main component - ganoin. This is a shiny substance that is a shiny layer of enamel-like dentin. It has significant hardness. Below is the bone. Thanks to this structure, placoid scales not only perform a protective function, but also serve as the basis of muscles, giving the body elasticity.
Bone scales, which are monogenic in composition, are of two types. Cycloid covers the body of herring, carp and salmon. Its plates have a rounded rear edge. They overlap each other like tiles, forming two layers: cap and fibrous. Nutrient tubules are located in the center of each scale. They grow with a cap layer along the periphery, forming concentric strips - sclerites. From them you can determine the age of the fish.
On the plates of the ctenoid scale, which is also a kind of bone scale, small spikes or ridges are located along the posterior edge. They provide the hydrodynamic abilities of fish.
How many years, how many winters…
Everyone knows that the tree rings on the trunk can determine the age of a tree. There is also a way to determine the age of fish by scales. How is this possible?
Pisces grow throughout their lives. In summer, the conditions are more favorable, since there is enough light, oxygen and food. Therefore, during this period, growth is more intense. And in winter, it slows down significantly or stops altogether. Activation of the exchange processsubstances causes the growth of scales. Its summer layer forms a dark ring, while its winter layer forms a white one. By counting them, you can determine the age of the fish.
The formation of new rings depends on a number of factors: fluctuations in temperature, amount of food, age and type of fish. Scientists have found that in young and mature individuals, rings form at different times of the year. For the first, it happens in the spring. Adults at this time only accumulate substances for the summer period.
The period of formation of annual rings also depends on the species. For example, in young breams this happens in the spring, and in mature breams in the fall. It is also known that annual rings are also formed in tropical fish. And this is despite the fact that the seasons of the year, fluctuations in temperature and the amount of food are absent here. This proves that annual rings are the result of a combination of several factors: environmental conditions, metabolic processes and humoral regulation in the body of fish.
The best…
It would seem that what could be unusual in scales? In fact, many fish have unique characteristics. For example, coelacanth scales on the outside have a large number of bulges. This makes the fish look like a saw. No modern look has a similar structure.
A goldfish is called so because of the scales. In fact, this is a decorative form of silver carp. The first goldfish were bred in the 6th century in China by Buddhist monks. Now more than 50 breeds of this species are known with red, golden and yellow coloration.
At first glance,The eel is a fish without scales. In fact, it is so small that it is almost invisible. It is also hard to feel, as the skin of an eel produces a lot of mucus and is very slippery.
So, the scales of fish is a derivative of the skin. It is one of the features of the structure, which provides adaptation to life in the aquatic environment. Depending on the chemical composition, placoid, ganoid and bone scales are distinguished.
