< h1 class = "pgc-h-arrow-right" > scales of 1 fish</h1>
In the process of evolution, most fish have two natural defense barriers, one is mucus and the other is scales. In the process of evolution, the two have antagonistic, mucus-rich fish species, the scales are relatively degenerate, such as the yellow jawfish, while the scales of the well-developed fish, its mucus is relatively small, because it is protected by the scales.
In the same way, some fish species, but another way, such as electric rays, can discharge, can be electric shock to protect themselves, these are actually in the process of fish evolution, survival of the fittest, the result of natural selection. There are three types of fish scales, namely shield scales, hard scales, and bone scales.
Shield scales are the oldest fish unique scales, its existence is earlier than the shark, that is, to the ancient soft body fish characteristic, the scales are very small, at first glance, can not see the scales, but with the hand from the back of the fish body forward, you can feel the obvious rough like sandpaper feeling.
The scales are made up of the epidermis and dermis together, the basal plate is buried in the skin, and the spiny tips are formed on the surface of the body facing backwards. Shield scales and human teeth in the occurrence of the same origin, similar structure, some scientists believe that shark teeth are also evolved from shield scales.
The second type of scale is the hard scale. Hard-scaled fish such as the finches, the body grows to a large, up to two or three meters long, is a carnivorous, but also an ancient fish, the fish eggs of this fish are poisonous and inedible. The whole body is covered with diamond-shaped fish scales, thick and hard, and arranged in rows, not in a tile-clad arrangement, like the armor worn by samurai, chimeric with convex and concave joints, leaving only a slight room for expansion and contraction at the junction. This way of scaly covering greatly hinders the fish from swimming, and over time, most fish are evolving to the next scale, that is, bone scales.
The third type of fish scale is bone scale. Most of today's fish scales belong to bone scales. The bone scales are divided into two layers, the lower layer is the elastic collagen fiber layer, and the upper layer is the bone layer containing a lot of calcium. The production of bone scales is composed of mesenchymal cells gathering under the germinal layer to form papillae, which later become osteoblasts and continuously secrete bone, forming bone flakes that are the original basis of the scales. Then the bone cells in the center of the protope disappear and exist only at the edges of the primordial, causing the upper layer of the scales to expand in various outer circles. New layers of dermal cells appear on the upper and lower sides of the scales, forming sachets that surround the scales.
All the scales are arranged in a tile-clad arrangement, whether exposed or covered, and are wrapped in scale sacs. Once the scale sac is damaged, bacteria will infect the fish body through the scale sac, so usually during my fishing process, even if I see that the surface of the fish is intact, I still require disinfectant to disinfect and sterilize, which is the principle here.
Bone-scaled fish, there is also a characteristic scale, that is, lateral scales. Lateral line scales are actually the sensory organs of fish, which are divided into the head and trunk, and have lateral line holes in the scales, which are then connected by lateral line tubes, and eventually converge on the fish's brain like a mesh line.
The lateral scales that we usually look at are actually dotted lines arranged by many lateral line holes. Lateral scales are often used as an important basis for identifying fish.
< h1 class = "pgc-h-arrow-right" > the blood of 2 fish</h1>
If you have a full understanding of the blood of fish, you will feel why nature is so amazing that it has evolved such a complex blood system.
The reason why fish can move and live endlessly is because the fish has a flawless vascular system, providing kinetic energy from the heart, pumping blood out of the heart, passing through the gills of the fish, loading hemoglobin with oxygen, transporting it to the various organs of the fish body, after exchanging nutrients and oxygen, the waste metabolized by these organs is collected into the heart through veins.
This perfect closed-tube single cycle has realized the stability of the fish body environment, the transportation of nutrients, and the metabolism of waste and hormones, the scientific and reasonable connection of various organs, the regulation of supply and demand, and the adaptation of the external environment, internal cell immunity, humoral immunity and blood coagulation regulation, etc., such a complex life project, have to make people sigh!
The blood and tissue fluid in the fish body are collectively referred to as extracellular fluid, which is the environment in which cells are directly bathed and lived, that is, the internal environment of the fish body. Blood belongs to connective tissue and is composed of plasma and various blood cells.
In general, the more fully evolved fish, the lower the blood ratio in their bodies, and the amount of fish fish is lower than that of vertebrates, such as mammals accounting for 7.5%-8% of body weight, while the blood volume of cartilaginous fish accounts for 5%, and the blood volume of teleost fish is 1.5%-3%.
Fish's blood contains a large number of blood cells, except for the blood cells, the rest is plasma, plasma is composed of a large amount of water, inorganic salts, proteins, various nutrients and metabolites.
The macro elements of inorganic salts in plasma are sodium, chlorine, potassium, calcium, magnesium, phosphorus, trace elements such as iron, copper, zinc, manganese, etc., and their role is to participate in the osmotic pressure regulation of the fish body, metabolism, and maintain the normal physiological functions of the cells.
The proteins in the plasma are subdivided into albumin, which maintains the osmolality of fish colloids, globulins, which are involved in immune epidemic prevention and lipid transport, and fibrin, which is involved in blood clotting and protects against damage. In addition, plasma also contains yellowish serum and hormones involved in the regulation of body fluids.
All vertebrate blood cells have blood cells, fish is no exception, fish blood cells according to their morphology and function can be divided into three categories, one is red blood cells, the other is white blood cells, and the third is thrombotic cells.
Fish erythrocytes have three characteristics: one is nucleated, oval in shape, and the size varies depending on the type of fish. In general, the more advanced the evolution, the smaller the red blood cells. For example, the red blood cells of the bony fish are smaller than those of the cartilaginous fish.
The second is that fish contain many immature red blood cells in their blood, which is different from other vertebrates.
The cytoplasm of red blood cells contains hemoglobin, which is a functional protein that transports oxygen and carbon dioxide. When these hemoglobin, which contains ferrous ions, is oxidized, it loses its ability to carry oxygen. Poor water quality, high nitrite, fish are easy to float, there are hemoglobin oxidation factors.
In the blood of fish, the largest proportion is red blood cells, in addition, it is white blood cells that account for one-tenth of the total number of blood cells. Individuals with white blood cells are larger than red blood cells, but can do deformed movements, and can swim outside the blood vessels to perform phagocytosis; inside the blood vessels, antibodies can be produced and play an immune role.
In terms of classification, according to the presence or absence of particles in white blood cells, white blood cells can be divided into two categories: granular white blood cells and particle-free white blood cells, and the particles of white blood cells are subdivided into basophils, neutrophils and eosinophils.
The blood of fish is also like a human, with platelets that play a coagulation role, called thrombotic cells, the individual is smaller than the red blood cell, there is a nucleus in the center, and the whole cell looks like two eggplant sets of about the same size stacked together.
Fish blood production is mainly in the spleen and kidneys, but connective tissue stem cells in organs such as intestinal mucosa, liver, blood vessel wall, and esophagus can also produce blood cells. The reticuloendothelial stem cells of these organs first generate hematopoietic cells, and then differentiate into red blood cells, white blood cells and thrombotic cells.
Take the spleen as an example, the spleen is the most important hematopoietic tissue in the circulatory system, on the mesentery, near the liver, the long, dark red organ is the spleen, which is developed from the mesoderm. When the spleen is dissected, it is found that the spleen is a reticulated tissue, the outer membrane of connective tissue, the inner cortex is a red marrow, and the inner layer is a white marrow. The erythrome produced red blood cells and thrombotic cells, and the leukolypolytic leukocytes and lymphocytes.
< h1 class = "pgc-h-arrow-right" > the heart of 3 fish</h1>
The heart is a very magical organ, when the fish hatches from the fish eggs, you can see the fish's heart beating.
Now there are two criteria for medical determination of death, one is brain death, and the other is that when the heart stops beating for more than half an hour, the heart cannot re-beat, so as to determine death. When the fish's heart doesn't beat for more than 30 minutes, it means the fish is dead. When you usually make fish to eat, when you take the heart of the fish from the front of the belly of the fish, you will find that the heart of the fish will continue to beat for a while. When I was a child, I felt incredible, and it wasn't until I went to college that I learned that this was a rhythmic contraction of the fish's heart under the bioelectric regulation.
The heart of the fish is located in front of the abdominal cavity, in the peri-heart cavity below the gill arch. The flesh of this circumference is thick and thornless, and I usually like to eat fish in this part, the meat is tender and delicious. And this periocentric cavity is filled with peri-heart cavity fluid, and the fish's heart is in it. In order to better protect the heart, there is also a layer of epicardium on the periphery of the heart, and the heart and the epicardium are filled with pericardial fluid. Even if you use this structure to express raw eggs, they will not be broken.
The heart of a fish is an animal evolutionary primitive heart, consisting of four parts: the arterial cone, ventricles, atrium, and venous sinuses. Cartilaginous fish are arterial cones, while true bone fish are more fully evolved by expanding from the abdominal aorta into a cone-shaped arterial bulb. For example, the arterial bulb of the carp is the white part of the heart, the volume is smaller than the ventricle, there is no valve inside, the wall is muscleless and rich in elastic fibers, it cannot beat, but it can buffer the pressure generated by ventricular contraction, protect the capillaries of the gills, and make the blood flow continuously.
The ventricles and atrium are the sites where rhythmic contractions occur and the main parts that drive blood flow in the circulatory system. The ventricles of the carp are located behind the arterial bulb, and among the four chambers of the heart, the walls of the ventricles are the thickest. The atrium is connected to the ventricles and the walls are thinner than the ventricles. The venous sinuses are located on the back side of the heart, the front is communicated with the atrium through the sinus foramen, the sinus wall is very thin, only a very thin layer of myocardium, the inner cavity is larger, and the blood of the various organs in the body flows into the venous sinuses through the total main vein, hepatic vein, etc., and through the contraction of the venous sinuses, the blood is pressed into the atrium.
In the heart, there are connective tissue valves in the sinuses and atrium, atrium and ventricle, and ventricular and arterial trunks, which function like a rubber valve in a water pipe, which raises blood pressure and prevents blood flow back.
This perfect blood circulation system makes the blood in the fish body cycle back and forth, flowing in the body of the fish, transporting nutrients and oxygen to each part of the fish body, and then through the capillaries that cover the whole body, the material exchange between the blood circulation system and the intercellular fluid is realized, like this output through the aorta, after reaching the organ, through the capillaries, and then collected by the veins, and finally back to the heart Of this process, similar to the water on the earth, through the surface runoff, air transpiration, and finally become rainwater, Back to the surface runoff and into the sea. What an amazing process!
The source of this article: Fish Farming Classic, authors: Xiao Jianchun, Xiao Jiancong, Luo Hong, please indicate the source when reprinting.