Who is the most famous aquatic creature? Of course, fish. But without scales, her life in the water would have been almost impossible. Why? Learn from our article.
Why fish scales
The integument of the body is 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 streamlined body shape of the fish is attached precisely to the scales. And for some species, it is a reliable shield from the teeth of the enemy.
Fish without scales practically does not exist. 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 bands. If the scales are not visible at all, it means that it is reduced. It develops in the dermis, or corium of the skin in the form of bone formations. In this case, a dense protective cover is formed. Examples of such fish are catfish, burbot, snakes, sterlet, sturgeon and lamprey.
Chemical composition
Fish scales are a bone or cartilage derivative of the skin. Half of its chemical elements are inorganic substances. These include mineral salts, namely phosphates and carbonates of alkaline earth metals. The remaining 50% is organic matter, represented by connective tissue.
Types of Fish Scales
Performing the same functions, skin derivatives are distinguished by their origin and chemical composition. Depending on this, several types of scales are distinguished. Representatives of the Cartilage class are placoid. This species is the oldest in origin. The skin of radiant fish is covered with ganoid scales. In bone, it has the appearance of scales that overlap one another.
Placoid Scales
This species of fish scale has been discovered in fossil species. Among modern species, its owners are stingrays and sharks. These are diamond-shaped flakes with a clearly visible spike that protrudes outward. Inside each such unit is a cavity. It is filled with connective tissue penetrated by blood vessels and neurons.
Placoid scales are very durable. In stingrays, it even transforms into thorns. It's all about its chemical composition, which is based on dentin. This substance is the basis of the plate. Outside, each flake is covered with a vitreous layer - vitrodentine. This plate is similar to the teeth of fish.
Ganoid and bone scales
Pisteper 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 using special joints. Their combination can be a whole shell, shields or bones on the skin. On the body, it is located in the form of rings.
This type of scale got its name from the main component - hanoin. This is a shiny substance that is a shiny layer of enamel-like dentin. It has significant hardness. Bone is located below. Thanks to this structure, placoid scales perform not only 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. Her plates have a rounded rear edge. They overlap each other like tiles, forming two layers: lid and fibrous. In the center of each flake are the nutritional tubules. They grow with a cap layer on the periphery, forming concentric strips - sclerites. On them you can determine the age of the fish.
On the plates of ctenoid scales, which is also a type of bone, small spikes, or ridges, are located on the posterior edge. They provide the hydrodynamic abilities of fish.
Long time no see...
Everyone knows that by the tree rings on the trunk, you can determine the age of the tree. There is also a method for determining the age of fish by scales. How is this possible?
Fish grow throughout life. 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. The activation of the metabolic process also causes the growth of scales. Its summer layer forms a dark ring, and the winter - white. 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 sexually mature individuals, rings form at different times of the year. For the first, this happens in the spring. Adult individuals at this time only accumulate substances by the summer period.
The period of formation of annual rings also depends on the species. For example, in young bream this happens in the spring, and in mature ones in the fall. The fact is also known that annual rings are formed in fish of the tropical zone. And this is despite the fact that the seasons, fluctuations in temperature and quantity 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.
Most most...
It would seem that what could be unusual in scales? In fact, it has unique characteristics in many fish. For example, the scales of coelacanth on the outside have a large number of bulges. This makes the fish look like a saw. No modern look has a similar structure.
And the goldfish is called so thanks to the scales. In fact, this is a decorative form of silver crucian carp. The first goldfish brought in the 6th century in China by Buddhist monks. Sechas is known for more than 50 species of this species with red, golden and yellow colors.
At first glance, eel is a fish without scales. In fact, he is so small that it is almost invisible. It is also difficult to feel to the touch, since the eel skin secretes a large amount of mucus and is very slippery.
So, fish scales are derived from 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.