"Scales" and "fish" are inseparable in our culture and cognition.
In speech and literature, not only "scales" are used to shape, but also "scales" refer to "fish".
Today, we will take a look at how interesting this layer of armor on the fish, this brocade coat, is.
Most fish have scales all over the body or locally, which are derivatives of the skin and play an important protective role in the fish body.
The scales of the fish, some of which are very large, such as the scales of the large Cao whitefish are 5 cm wide, and are almost the largest of all the single-layer scales of the bony fish. Some fish are not large in their own right, and their scales are of course smaller, less than 1 millimeter wide.
▲ Anchovy, commonly known as Cao whitefish, pictured is the long carp, Ilisha elongata
Source: Taiwan Fish Database
The scales of fish have many shapes, and the scales of general bony fish such as catfish and scorpionfish are mostly round and small, slightly elastic, arranged in a single layer, called "single layer scales".
Left: Catfish, Silurus asotus; Right: Poirot, Pterois volitans
There are no two identical fish scales in the world
According to its appearance, structure and occurrence characteristics, fish scales can be divided into two types: shield scales and bone scales.
▲ Type of fish scales, A. shield scales (sharks); B. hard scales (garnets)
C. Round scales (carp) ;D. Ctenophores (yellow perch)
Shield scales are endemic to cartilaginous fish, formed by the epidermis and dermis, arranged in an approximate diagonal line, which can effectively reduce the resistance of water bodies.
The sharks in the cartilaginous fish are covered with shield-like "shield scales". Each shield scale has a bone nucleus (substrate) buried in the skin and a barb (scaly spine) that stretches backwards. If you touch it in the opposite direction with your hand, it will rub the skin.
▲ Shark scales under electron microscopy, the picture comes from the Internet
Teleost fish have bony scales, formed entirely from the dermis. Bone scales can be subdivided into hard scales, round scales, and ctenophores.
Typical representatives with hard scales are sturgeon, garnets and multi-finned fish, etc., whose scales are very hard and diamond-shaped, and the scales are closely connected by fibers between the scales and the scales.
▲ American sturgeon, Lepisosteus osseus
The image comes from the Taiwan Fish Database
▲ Long-snouted gar, Acipenser oxyrinchus
Round scales and ctenophores are found in higher bony fish, both arranged in a tile-like arrangement on the surface of the fish body. The round scales are rounded, the anterior area is buried in the dermis, and the free part of the posterior area is smooth and spineless, which is the scale of fish such as herring and needlefish.
▲ Pacific herring, Clupea pallasi
Image from FishBase
▲ Grass carp, known as the "four big fish", mostly have round scales
The image comes from the Internet
There are many small spines in the posterior area of the ctenophores, which are generally rough when touched by hand, and such scales are found in sea bass, yellow croakers and small yellow croakers. None of the extant hagfish and cephalotypes have scales.
▲ Japanese flower perch, Lateolabrax japonicus
▲ Yellow croaker, Larimichthys crocea
Function of the scales
Derivatives of the skin
Fish scales have a variety of functions for fish. First, the scales provide a layer of defense for the fish body that prevents microbes from invading the body, helping to fight disease and infection.
Exoskeletons Secondly, fish scales also play the role of exoskeletons, which can help fish maintain their body size. For higher fish, this function is not important because their scales are soft and thin. Again, fish scales can also play a camouflage role. The scales in the belly of the fish can reflect and refract light, and if there are fierce enemies swimming underwater, it is difficult to distinguish them from the sparkling water surface when you see the shiny abdomen. In addition, some fish scales are also self-defense weapons. The spines on the stingers are slowly evolved from fish scales, and whenever the enemy attacks, its stomach becomes bulging, and the spines are also erect, like a hedgehog, and the enemy sees this situation and feels that he cannot put his mouth down, so he has to give up the idea of eating it.
▲The picture shows the dimly spotted pufferfish, Diodon hystrix
The picture comes from the Taiwan Fish Database, and the right picture comes from the Internet
How can fish scales be eaten?
The shape, size, number and arrangement of fish scales are relatively fixed for various fish, so they are often used as the main basis for identifying species.
In addition, similar to the tree rings, due to the influence of water temperature, bait and other factors, the growth of fish throughout the year is not balanced, and correspondingly different wheel belts are formed on the scales, and experienced fishermen can measure the age and growth of fish.
▲Schematic diagram of the surface structure of the scales of fish, picture from the network
Fish scales are an important reference for the research work of ichthyologists.
The number of scales grown in parallel with the lateral line is called the "number of columns", and the number of scales arranged from the back to the abdomen is called the "number of rows".
The number of columns and rows of scales on each fish is different, which is an important basis for identifying fish. Fish scales are also a basis for ichthyologists to infer the age of fish.
In the first year of life, fish are covered with scales, which are thick in the middle and thin at the edges, resembling a dwarf cone with a truncated spire, and many concentric rings like the cross-section of a tree.
Understanding the age of fish can calculate the average annual growth rate and mortality rate of fish, so as to help aquatic workers to presume the age composition of fish stocks, so that fishing is timely, catch large and small, and protect and rationally use aquatic resources.
In addition to using scales to calculate age, salmon produced in northeast China can be inferred in age by gill covers; flounder produced along the coast of China can also be inferred in age by vertebrae.
In addition, fish scales can also be eaten, but instead of eating a piece of fish scales, it is boiled out of the frozen, that is, fish scale jelly.
Wash the scales of grass carp or carp, put them in a pot with green onion and ginger and boil them, and then fish the scales after the collagen is boiled, let the soup cool and freeze into freezing, mix with the sauce, Q bomb refreshing.
▲ Fish scale jelly, the picture comes from the Internet
Fish scales are rich in protein and a variety of minerals, including a large amount of raw gum, which is the secret of fish scales.
At present, the most important use of fish scales is to extract collagen and use as poultry feed powder. Collagen is used in food, medicine, cosmetics and other fields, such as making new heart biological valves, prolonging the service life of materials, alleviating patient pain, etc.
In addition, researchers have also successfully extracted gelatin, collagen peptides, nano-biological hydroxyapatite (HAP nanoparticles), thioguanine and other organic matter with important edible and medical value from fish scales.
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