What are fish skin derivatives?

The main derivatives of fish skin are probably mucus glands, poison glands, pigment cells, fins, scales, pearls and so on.

It is characterized by thin and soft epidermis, no stratum corneum structure and many glandular cells differentiation. The dermis is mainly composed of connective tissue, with a large number of pigment cells, blood vessels and nerves. The function is to defend against mechanical damage, chemical damage, feel the change of external environment and resist the entry of microorganisms and parasites.

The skin of fish is actually the same as that of other vertebrates. There are two layers: the outer layer is called epidermis and the inner layer is called dermis. In addition, fish skin has a special gland, which can secrete a lot of mucus and make the skin sticky. The amount and composition of mucus vary with the species of fish: for example, if a blind eel is put in a bucket, the water will soon turn into a milky colloidal liquid, but this will not happen in other fish. Fish's skin is surrounded by different scales, which are formed by the gradual deposition of calcium in body tissues in the dermis. Fish scales play a role in protecting the skin. Generally speaking, fish scales are divided into shield scales, round scales, comb scales and hard scales.

The scales on the shield are bone matrix buried in the skin, while the exposed spines have enamel. Among cartilaginous fish, sharks and fish are covered with scales. Shark skin with shield scales is not only very strong but also very tough, and can be used for tanning or making various decorations.

Round scales are common carp, which is round scales. Similar to human nails, the front ends of scales extend into the dermis, and the rear ends are all exposed, which are arranged regularly layer by layer, much like tiles on the roof.

The main feature of comb scale is that the back edge of scale is serrated. There are many fish belonging to the comb, such as yellow croaker, sea bass, red snapper and so on. Interestingly, flounder, flounder, has two scales, the colored side of the body is a comb, and the colorless side is a round scale; There is also a fresh grouper, which also has two kinds of scales. The scales above the lateral glands are comb scales, and the scales below the lateral glands are round scales. However, it should be mentioned here that there are exceptions in some cases: for example, the back end of the round scale has also become wavy; The back end of the comb scale is also soft and round.

Hard scale: this scale is diamond-shaped and consists of three layers of tissue, with a layer of bright enamel on it, which is called hard scale, hence the name of hard scale; The lower layer is a thicker bone layer with a whole row of microvessels in the middle. However, the special structure of this hard scale makes the fish bend easily. The main representative of scleroderma is bowfin fish, which no one has ever seen. However, its offspring is sturgeon, and now you can see a row of hard scales on the upper edge of its tail fin. According to fish fossils, it was gradually developed at first, and then gradually degenerated.