Fish scales

During the evolution of fish, most of them have two natural defense barriers, one is mucus and the other is scales. In the process of evolution, the two are antagonistic. Fish species with more mucus have relatively degraded scales, such as yellow catfish; while fish with well-developed scales have relatively less mucus because they are protected by the scales.

In the same way, some fish species have taken a different approach. For example, the fish of the electric rays can discharge electricity and protect themselves by electric shock. These are actually the result of natural selection in the evolution of fish, the survival of the fittest. There are three types of fish scales: shield scales, hard scales, and bone scales.

Shield scale is a kind of scale unique to ancient fish. It existed earlier than sharks. It is unique to ancient soft fish. The scales are very small. At first glance, the scales are not visible, but they can be seen from the fish by hand. Stroking the back of the body forward, you can feel a clear rough sandpaper-like sensation.

The scales are composed of the epidermis and the dermis. The basal plate is buried in the skin, and the squamous spines point backward to form spinous processes on the body surface. Shield scales are homologous to human teeth and have similar structures. Some scientists believe that shark teeth also evolved from shield scales.

The second type of scale is hard scale. Boxfish, such as gar, grow to a very large body, up to two or three meters long, and are carnivorous. They are also ancient fish. The eggs of this fish are poisonous and cannot be eaten. The whole body is covered with diamond-shaped fish scales, thick and hard, and arranged in rows, not covered with tiles, like armor worn by a samurai, with convex and concave joints interlocking, leaving only a little room for expansion and contraction at the joint. This kind of scale covering method greatly hinders the fish's swimming. Over time, most fish are evolving to the next kind of scale method, that is, bone scales.

The third type of fish scale is the bone scale. The scales of most fish nowadays belong to bone scales. The bone scale is divided into two layers, the lower layer is a layer of elastic collagen fibers, and the upper layer is a bone layer with a lot of calcium. The formation of bone scales is formed by the collection of mesenchymal cells under the germinal layer to form papillae, which later become osteoblasts and continue to secrete bone, forming bone flakes, which are the primordia of scales. Then the bone cells in the center of the primordium disappear and only exist on the edge of the primordium, making the upper layer of the scales continue to expand in circles. New dermal cell layers appear on the upper and lower sides of the scales, forming squamous sacs surrounding the scales.

All the scales are arranged in a tile-covered manner, whether they are exposed or covered, they are all wrapped in a scaly sac. Once the scaly sac is damaged, bacteria will infect the fish body through the scaly sac. Therefore, in my fishing process, even if I see that the surface of the fish is intact, I still require disinfection and sterilization with disinfectants. This is the principle.

Bone scale fish, there is also a unique scale, that is the lateral line scale. The lateral line scales are actually the sensory organs of the fish, which are divided into the head and trunk. The lateral line holes are opened on the scales, and then these small holes are connected by the lateral line tube, and they are collected into the fish's brain like a network cable.

The side line scales we usually look like are actually dotted lines arranged by many side line holes. Lateral line scales are often used as an important basis for identifying fish.

Fish blood

If you have a full understanding of the blood of fish, you will feel why nature is so miraculous that it has evolved such a complicated blood system.

The reason why fish can move and live endlessly is because the fish has a vascular system. The heart provides kinetic energy, pumps blood out of the heart, passes through the fish gills, loads hemoglobin with oxygen, and transports it to the various organs of the fish body. After nutrition and oxygen, waste products metabolized by these organs are collected to the heart through the veins.

This closed-tube single cycle realizes the stability of the fish’s internal environment, the transportation of nutrients, and the metabolism of waste and hormones, scientifically and rationally connects the various organs, regulates supply and demand, and realizes the external environment. The adaptation to internal cell immunity, humoral immunity and blood coagulation regulation, such a complicated life engineering, I have to sigh!

The blood and tissue fluid in the fish body are collectively referred to as extracellular fluid, which is the environment in which cells directly bathe and survive, that is, the internal environment of the fish body. Blood belongs to connective tissue, which is composed of plasma and a variety of blood cells.

Generally, the more fully evolved fish, the lower the blood ratio in their body, and the fish volume is lower than that of vertebrates. For example, the blood volume of mammals accounts for 7.5%-8% of body weight, while cartilaginous fish The blood volume of the class is 5%, and the blood volume of bony fish is 1.5%-3%.

Fish's blood contains a large number of blood cells. Except for blood cells, the rest is plasma, which is composed of a large amount of water, inorganic salts, protein, various nutrients and metabolites.

The major elements of inorganic salts in the plasma are sodium, chlorine, potassium, calcium, magnesium, and phosphorus, and the trace elements are iron, copper, zinc, manganese, etc., which are involved in the regulation of osmotic pressure, metabolism of the fish body, and the maintenance of normal cells. Physiological function.

The protein in plasma is subdivided into albumin, which maintains the osmotic pressure of fish colloid, globulin, which participates in immune prevention and lipid transport, and fibrin, which participates in blood coagulation and protects against injury. In addition, the plasma also contains light yellow serum and hormones involved in body fluid regulation.

There are blood cells in the blood of all vertebrates, and fish are no exception. Fish blood cells can be divided into three categories according to their shape and function. One is red blood cells, the other is white blood cells, and the third is thrombus.

The red blood cells of fish have three characteristics: First, they are nucleated and oval in shape. The size varies with the type of fish. In general, the higher the evolution, the smaller the red blood cells. For example, the red blood cells of bony fish are smaller than those of cartilaginous fish.

The second is that fish blood contains many immature red blood cells, which is different from other vertebrates.

The third is that the cytoplasm of red blood cells contains hemoglobin, which is a functional protein that transports oxygen and carbon dioxide. When these hemoglobins containing ferrous ions are oxidized, they lose their oxygen-carrying capacity. Poor water quality, high nitrite, fish are prone to floating heads, there is a factor that hemoglobin is oxidized.

In the blood of fish, red blood cells account for the proportion, besides that, white blood cells account for one-tenth of the total number of blood cells. Individuals of white blood cells are larger than red blood cells, but they can perform deformation movements and swim outside the blood vessels to perform phagocytosis; inside the blood vessels, antibodies can be produced to play an immune role.

In terms of classification, according to whether there are granules in the white blood cells, white blood cells can be divided into granular leukocytes and non-granular leukocytes. At the same time, granular leukocytes are subdivided into basophils, neutrophils and eosinophils.

Fish's blood is also like humans. There are blood clotting platelets called thrombus cells. Individuals are smaller than red blood cells and have a nucleus in the center. The whole cell looks like two eggplants of the same size stacked together.

Fish blood is mainly produced in the spleen and kidneys, but the connective tissue stem cells in the intestinal mucosa, liver, blood vessel wall, esophagus and other organs can also produce blood cells. The reticuloendothelial stem cells of these organs first generate blood cells, and then differentiate into red blood cells, white blood cells and thrombus cells.

Take the spleen as an example. The spleen is an important hematopoietic tissue in the blood circulation system. On the mesentery, near the liver, the long, dark red organ is the spleen, which develops from the mesoderm. When the spleen is dissected, it will be found that the spleen is a reticular tissue surrounded by connective tissue membranes, the inner cortex is red red pulp, and the inner layer is white pulp. Red iliac produces red blood cells and thrombus cells, and white pulp produces white blood cells and lymphocytes.

Fish heart

The heart is a very magical organ. When a fish hatches from a fish egg, you can see the fish's heart beating.

There are two current medical criteria for determining death. One is brain death, and the other is that when the heart stops beating for more than half an hour, the heart cannot resume beating, so as to determine death. When the fish's heart does not beat for more than 30 minutes, it means that the fish is dead. When you usually make fish to eat, when you take out the fish's heart from the front of the fish's abdomen, you will find that a magical thing is that the fish's heart will continue to beat for a while. When I was young, I found it incredible. I didn't realize that it was the rhythmic contraction of the fish's heart under the regulation of bioelectricity until I was in college.

The heart of fish is located in the front of the abdominal cavity, in the peripheral cavity below the back of the branchial arch. The meat around the heart cavity is thick and without thorns. I usually like to eat fish from this part. The meat is tender and delicious. And this pericardial cavity is filled with pericardial fluid, and the fish's heart is in it. In order to better protect the heart, there is an epicardium around the heart, and the space between the heart and the epicardium is filled with pericardial fluid. Even if the raw eggs are delivered with this structure, they will not be broken.

The heart of fish belongs to the primitive heart in the evolution of animals. It consists of four parts, namely the arterial cone, the ventricle, the atrium and the venous sinus. Cartilaginous fishes are arterial cones, while true bony fishes are more fully evolved, they are conical arterial bulbs that expand from the abdominal aorta. For example, the arterial bulb of a carp is the white part of the heart. It is smaller in volume than the ventricle, has no valves inside, and the wall has no muscles but is rich in elastic fibers. It cannot pulsate, but it can buffer the pressure generated by ventricular contraction, protect the capillaries of the gills, and make blood. Continuous flow.

The ventricles and atria are the parts that can produce rhythmic contractions and are also the main parts that promote blood flow in the blood circulatory system. The ventricle of the carp is located behind the arterial bulb. In the four chambers of the heart, the walls of the ventricle are thick. The atrium is connected to the ventricle, and the wall is thinner than the ventricle. The venous sinus is located on the back of the heart, communicating with the atrium through the sinus vent in the front. The sinus wall is very thin, with only a very thin layer of myocardium, and a large internal cavity. The return blood from various organs in the body passes through the common main vein and hepatic vein. When it enters the venous sinuses, the blood is forced into the atria through the contraction of the venous sinuses.

In the heart, connective tissue valves exist in sinuses and chambers, chambers and chambers, chambers and arterial trunks. Valves function like rubber valves in water pipes to increase blood pressure and prevent blood from flowing back.

This blood circulation system makes the blood in the fish body circulate back and forth, flow in the fish body, transport nutrients and oxygen to every part of the fish body, and then realize the blood circulation system and cells through the capillaries all over the body. The material exchange of interstitial fluid, like this, is exported through the aorta. After reaching the organs, it passes through the capillaries, then collects by the veins, and returns to the heart. It is similar to the process of water on the earth through surface runoff and air transpiration. It turns into rainwater, returns to the surface as runoff, and flows into the sea. What an amazing process!

Source: Fish Farming

Author: Xiaojian Chun Luo Hong Xiaojian Cong