Fish are aquatic, cold-blooded vertebrates that breathe through gills and have jaws and fins. Extant fish can be divided into two main groups: cartilaginous fish (such as sharks) and bony fish (fish with linear and undulate fins). Both groups of fish first appeared in the early Devonian. The more advanced group of linear-finned fishes, called bony fishes, began to evolve during the Jurassic period and are now the most abundant fishes. There are also several extinct species of fish.
Fish have been with humans for more than 5,000 years, and have formed an unbreakable bond with them, becoming an extremely important food and ornamental pet in their daily lives, but people have no idea what kind of animal is a "fish". But people know little about what animals are "fish" and how fish should be defined. With the development of science, the definition of fish has changed a lot.
Nearly 500 million years ago, a major leap in the course of life on Earth, the emergence of the earliest fish-like animals, opened the prelude to the history of vertebrates, which led to the development of the animal kingdom, entered a new stage of history. The earliest true fish appeared more than 300 million years ago, throughout the long history of the process, has survived a large number of fish, has long been with the passage of time and extinction, today's survival of the fish on earth, is only the later emergence, evolution of a very small part of the species.
Humans were able to identify species a long time ago, to the name, usually referred to as "fish" includes all the animals in the water, and therefore many of the animals living in the water are named fish, whales, seals, salamanders (baby fish), squid, squid, octopus, starfish, jellyfish, sponges, amphibians, etc., and fish are mixed up. . In the end, those aquatic animals are the real "fish", for the division of "fish", in different generations have different definitions.
More than two thousand years ago, the ancient Greek philosopher Plato (427 - 347 BC) on the definition of fish is: "This class (fish) is made by the completely ignorant and unaware of things. The Lord of Transformations thought that it was no longer worthwhile to give pure breath in this class, because they are the offspring of all kinds of sins, and there exists an impure heart. The Lord of Transfiguration threw them into the water so that they might breathe that divine and pure air through the deep sludge. This is how fish and oysters and all other aquatic animals, as having received punishment for the great sin of ignorance, were separated remotely." Plato's view is full of creationism. Thanks to the development of modern science, this view has long been completely rejected.
China's "Er Ya" in the early Han Dynasty divided animals into four categories: worms, fish, birds and beasts, of which fish include fish, amphibians, reptiles and other lower vertebrates and whales and shrimps, crabs, shellfish, etc.
In the 18th century, the Swedish naturalist Linnaeus (1707 - 1778) founded the modern taxonomy. In his book "System of Nature", he divided the animal kingdom into six classes: mammals, birds, amphibians, fish, insects and worms, etc. In 1859, Darwin, a British biologist, published his book "The Origin of Species", which gave birth to systematic taxonomy. From then on, the definition of fish and the scope of inclusion is also determined.
In fact, those animals belong to the "fish"? Modern taxonomists define "fish" as vertebrates that live in water all their lives, breathe through their gills, and swim with their fins. Fish include the three major groups of the Orthostomatidae, Chondrichthyes, and Sclerostomatidae. There are more than 26,000 known species of fish in the world, which is the largest group of vertebrates, accounting for 48.1% of the total number of vertebrates. The vast majority of them live in the ocean, and there are about 8600 species of freshwater fish. China's existing fish nearly 3,000 species, of which about 1,000 species of freshwater fish.
In the coarse sand of the shallow coastal near-shore area in China, there is a slender body shape, not more than 50 millimeters long, the two ends of the pointed, translucent small "fish", whose scientific name is "Wenchang fish", although its appearance is a fish, but it does not belong to the fish, the dorsal side of the body, although it is a fish, but it does not belong to the fish. Although it looks like a fish, it does not belong to a fish. Although the dorsal side of the body of the amphioxus has a spinal cord, there is no spinal structure, no skeleton in the body, no obvious head, and the heart is not formed. Amphioxus near fish features are mainly manifested in the presence of the notochord, neural tube and gill slits, in taxonomy in the invertebrates and vertebrates in the middle of the transitional taxa - protocordata of the class of holothurians, also known as the headless class.
Fish have special features
The fish will sound Kangji carp will make a "bark" sound; electric catfish screams like a cat's wrath; box triggerfish can make a dog barking; pomfrets gills screaming sometimes like a pig, sometimes like a moan, and sometimes like a snore; seahorses will make a monotonous sound like a drum. Stonefish are known for their good calls, which sound like rolling, drumming, the flight of a hummingbird, catcalls and whistles, and their calls are especially common during reproduction for the purpose of clustering.
Fish that generate electricity
Fish that generate electricity Some fish can generate electricity from their bodies, and the voltage they emit is several times greater than the voltage of the electricity we use in life. There are about 500 species of fish with the ability to generate electricity, such as electric eels, electric catfish, electric eels, longnose fish and so on.
A variety of power generation fish, they send out the current strength and voltage are different. Electric ray body and flat and garden, with a long tail, like a fan. Electric catfish living in the Nile River in Africa, the body is only 1 meter long, but can send out 350 volts of high voltage electricity. Fish
will glow fish some fish glow, for example, China's southeastern coast of the banded fish and dragonfish is attached by the body of the light-emitting bacteria issued by the light, while more fish glow is issued by the fish itself by the light-emitting organs of the light.
Candlefish have multiple rows of luminous organs on their abdomen and ventral side, like rows of candles, so they are called candlefish. The back of the head of the deep-sea bald fish is flattened, and is covered by a pair of very large luminous organs, and the large luminous organs may play a role in vision.
The tree-climbing fish climbing perch inhabits still, slow-moving, silty water bodies. When the water body dries up or the environment is not suitable, often rely on swinging gill cover, pectoral fins, turn over and other methods to climb over the bank, slope, move to a new body of water, or lurking in the mud. Climbing perch's gill epiglottis is very developed, can breathe air, so away from the water for a longer period of time without dying, when the water body lack of oxygen, away from the water, or in a slightly moist soil can live for a longer period of time. Climbing perch to small fish, shrimp, zooplankton, insects and their larvae for food. In order to catch airborne insects, often rely on the head of the developed spines, gill covers, pectoral fins and other organs to climb up the shoreline bushes.
Flying fish swallow skate body long and flat round, slightly pike-shaped. General body length of 20-30 centimeters, weighing 400-1500 grams. The back is quite wide, the sides are flat to the tail gradually thin, the ventral surface is very narrow. The head is short, the muzzle is short, the eyes are large, and the mouth is small. The teeth are fine, and the upper and lower jaws are narrowly banded. The dorsal fin is located at the back of the body opposite the anal fin. The pectoral fins are extraordinarily long and broad, reaching the end of the anal fins; the ventral fins are large and posterior, reaching the end of the anal fins. Both fins are extended like dragonfly wings.
Fish have gills to breathe in the water, and swim bladders to sink and float freely in the water. But is it true that some people say that fish that live in water can also drown?
Although this sounds ridiculous, it is true. The swim bladder is a "life preserver" for the fish when it swims, and it can be inflated and deflated to regulate the specific gravity of the fish body. In this way, the fish requires only minimal muscle activity when swimming, and can maintain a stable state in the water without sinking or floating. However, when the fish sinks to a certain depth (i.e., the "critical depth"), the enormous pressure from the outside world makes it impossible for it to wither the volume of the swim bladder. At this time, it is subject to buoyancy is less than its own gravity, so it involuntarily sinks to the bottom of the water, no longer float, and ultimately drowned because of the inability to breathe. Although the fish can still float by swinging its fins and tail, it is useless if it sinks too deep.
On the other hand, fish that live in the deep sea can live freely in deep water because their bones can withstand a lot of pressure. If we get a deep-sea fish above the "critical depth" quickly, it will "expand" until it rises to the surface, because the pressure inside its body is not balanced by the lesser pressure outside. Sometimes, it will even spit out its internal organs and "explode" and die.
Editing the purpose of each part of the fish
The role of the fins
Dorsal fin: keep the fish on its side, plays a key role in the balance of the fish, if it is lost, it will be out of balance and tipped over on its side.
Pectoral and ventral fins: balance, if lost, the fish will sway from side to side.
Caudal fin: determines the direction of movement, if lost, the fish will not turn.
The anal fin: coordinates the other fins and acts as a counterbalance; if it is lost, the body will sway slightly.
The fins also have the function of sensing the water flow, so they can not be lost.
Nine belly fish:
The scientific name of the nine belly fish is dragonfish, belonging to the family of dogfish, also known as dogfish, shrimp gurgling, bean curd fish, dog spit fish, dog's milk, water dragonfish and so on. Why is the head of the fish called nine belly fish? It is quite interesting to say. The dragonfish called dog mother fish (or dog spit fish) is a common Cantonese masters called, perhaps because the food industry called dog mother fish, dog spit fish is too difficult to hear, coupled with the Cantonese pronunciation of "dog" is easily mistaken for "nine", "mother", "mother", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog", "dog". "mother", "spit", and the pronunciation of "belly" is similar, so the master of the kitchen will be called "nine belly fish
Nine belly fish body long and sideways flat, generally about 15 to 26 centimeters, weighing about 75 to 150 grams. Head large, small eyes, mouth cleft is quite large, two jaw teeth are densely packed, teeth fine and sharp. The body is soft, mostly smooth and scale-free, except for a line of larger scales on the lateral line directly to the caudal fork, the head and dorsal line is brown, the abdomen is creamy white, one dorsal fin, only fins without fin spines, a small adipose fin after the dorsal fin, pectoral and ventral fins are well developed, about equal in length. The pectoral and ventral fins are well-developed and about equal in length. The caudal fin is tridentate with a shorter middle lobe. Nine-bellied fish are mainly distributed in the Indian and Pacific Oceans. China's South China Sea, the East China Sea and the southern Yellow Sea are produced, including Wenzhou, Zhejiang Province, Taizhou and Zhoushan offshore as well as the coast of Fujian yield more, the catch period in the spring. Nine belly fish is a "light death" fish, fishing off the sea on the shore will die, but also because of its body contains more water, not easy to store, so before the more processed into salt dry products, that is, "dragon's head baked".
Fish with rich nutritional value
Fish protein content of about 15 to 24%, so fish is a very good source of protein, and these proteins have a high absorption rate, about 87 to 98% will be absorbed by the body. The fat content of fish is much less than that of animal meat, and fish contains very special omega-3 fatty acids, such as EPA (Ecosapenoic acid, eicosapentaenoic acid) and DHA (Decosahexanoid acid, docosahexaenoic acid).
In addition, fish oil is rich in vitamins A and D, especially in the liver of fish. Fish also contains water-soluble vitamins B6, B12, niacin and biotin. Fish also contains minerals, the most noteworthy such as cloves or sardines, if eaten with the bones, is a good source of calcium; saltwater fish is rich in iodine; other such as phosphorus, copper, magnesium, potassium, iron, etc., can also be ingested when eating fish.
DHA is a key element in promoting brain power
Why do you often hear that eating fish makes you smarter? There is actually a scientific basis. The DHA contained in fish is mainly found in the brain, retina and nerves. DHA can maintain the normal function of the retina, and infants especially need this kind of nutrient to promote the sound development of eyesight; DHA is also a great help to the development of the human brain and the development of intelligence, and it is an indispensable nutrient for the growth of the nervous system.
Generally, seafood contains DHA, but deep-sea fish such as salmon, mackerel, sardines, swordfish, and anchovies are the most abundant, especially in the fatty tissues near the eyeballs of fish. Cod, lice and otter are high in fat but not very high in omega-3 series fatty acids; tuna, yellowtail, sea bass and whitebait are even lower in omega-3 series fatty acids.
DHA is even more important for the rapid brain development of fetuses and infants. Infants are unable to produce enough DHA on their own for brain cell and neurological development, and must obtain their DHA from breast milk or infant formula. The DHA content of breastmilk is rich, and breastfed babies have better visual development and cognitive development than those fed infant formula. The longer the babies are breastfed, the higher their IQs are, and the better their academic performance is.
However, if mothers do not consume enough DHA-rich foods during pregnancy or lactation, their bodies will not contain enough DHA, and the concentration of DHA in their babies may be insufficient. Therefore, pregnant and lactating women should consume more deep-sea fish to increase the amount of DHA in their bodies during pregnancy, or pass it on to their babies through breastfeeding. If it is inconvenient or you don't like to eat fish, you may have to consider taking capsule-type DHA supplements. If a mother is unable to breastfeed or stops breastfeeding, it is better to add DHA to the infant's diet, such as choosing DHA-enriched formula, or using more fish as a side dish, but some infant formulas don't have DHA added to them, so it is important to pay attention to the labeling when purchasing them.
People suffering from Alzheimer's disease have an average of 30 to 40 percent less DHA in their blood than normal people, and those who eat fish are less likely to suffer brain degeneration, and may even be able to improve the symptoms of Alzheimer's disease. Even for healthy people in general, the lack of DHA can cause a decrease in memory and learning ability.
Medical evidence suggests that eating fish has many benefits
Fish is rich in proteins that can help young children, children and adolescents to grow and develop, and can also help recovery and healing when they are sick or have wounds. And fish protein, muscle fiber structure is relatively short, connective tissue is also less, so the fish eat more than other animal meat meticulous tenderness, but also easier to digest, very suitable for young children and the elderly to eat. Fish contains less fat than animal meat, so the calories are lower than animal meat.
Medical research has found that the proportion of Eskimos suffering from cardiovascular disease is very low, because their diet has a large number of marine fish rich in EPA and DHA; in the Japanese region of the survey, also found that the residents of the coastal fishing villages, the proportion of cardiovascular disease is lower than the proportion of farmers in the Mainland. The EPA and DHA in fish are two special omega-3 fatty acids that can lower blood lipids, especially triglycerides and LDL cholesterol (bad cholesterol), and will make platelets less likely to coagulate, and have the effect of preventing thrombosis caused by cardiovascular disease and stroke, which can protect the heart.
A Finnish study found that people who ate fish less than once a week suffered from mild depression, a higher percentage than those who often ate fish, because the EPA and DHA in fish can eliminate anxiety and prevent schizophrenia. In short, eating fish can make people healthier and smarter.
The pharmacological effects of fish scales
Most fish, the whole body clad in armor-like scales, and scales have three functions:
(l) in the fish belly scales, silver, can reflect and refract bright light, like a mirror, so that the bottom of the ferocious aquatic animals dazzle, produce a color of the sky and water, do not identify the object, to become a natural camouflage.
(2) The scales provide a protective barrier for the fish, isolating it from the countless microorganisms around it, effectively avoiding infection and resisting disease.
(3) Scales provide a layer of external skeleton for the fish, which keeps the fish body in a certain shape and reduces friction with the water. In addition, biologists based on the scales on the ring of the annual cycle (each round represents a winter), to know the age of the fish; can also be more accurate grasp of its growth, mortality and health.
Fish scales, accounting for 2% to 3% of a fish's body weight. The main characteristics of the scales: transparent from the outside, like petals, and the edge of the tiny curls; white gloss; slightly fishy smell; firm and soft texture; water content range of 16-4% a 17.8%, an average of 17.5%. Nutritionists have found that fish scale is a special health food. It contains more ovalbumin, the fat globule decomposition into emulsion and water intermixing, have enhanced human brain memory, slowing down the role of cellular aging. Fish scales contain a variety of unsaturated fatty acids, can reduce cholesterol deposition in the blood vessel wall, promote blood circulation, and play a role in the prevention of hypertension and heart disease
. Fish scales are also rich in a variety of trace minerals, especially calcium, phosphorus content is high, can prevent pediatric sharecropping disease and the elderly osteoporosis and fractures.
Fish scale is the fish dermis collagen generated bone, the scientific name for fish scale hard protein. It is in the field of medicine, chemical industry, showing an extraordinary role. Extracted from fish scales 6 a rusty guanine, clinical treatment of acute hemorrhagic disease, the efficiency of 70% a 75%; and stomach cancer, lymphadenoma also has a miraculous effect. Extracted from the fish scales in the special industrial products - fish silver is an expensive biochemical reagents, used in the pearl decoration industry and paint manufacturing industry, domestic and foreign markets are very popular.
Looking at fish scales, a variety of nutritional health care substances in one, so foreign countries set off a "fish scales therapeutic fever". Fish scale cooking method is: first wash the fish body with water, scrape down the scale concentration, and then rinse with water to drain, put into the pressure cooker, add appropriate amount of vinegar (in addition to fishy), 500 grams of scales plus 800 grams of water, the proportion of high-fire cooking for 10 minutes, and then switch to the fire to cook for 20 minutes, out of the fire and decompression. Open the pot will be curled scales and miscellaneous scum fishing out, the liquid poured into the container, static condensation into the color gelatin protein. Make soup, with ginger, yellow wine, salt and green onion and other condiments, cut into pieces and then boiled Vicodin. If eaten cold, sugar, mint oil, cinnamon or sesame sauce,
chili oil as a condiment, cut into pieces and stirred to eat. I urge you to try the above method, you can taste the delicious dishes, but also to get the benefits of nourishment and fitness.
People eat fish, the fish scales scraped off and thrown away, it is too bad. It is a pity to throw away the fish scales. It is recommended that food factories or pharmaceutical factories should pay attention to the utilization of the fish scales, so as to create wealth for the society and to benefit the people.
The pharmacological effects of swim bladder
Fish bladder
(from the compendium of materia medica)
Synonyms of swim bladder ("Qimin want wood"), 鱁鯷, fish, white, swim bladder ("Gleanings of Materia medica"), fish gelatin ("San Yin Fang"), white swim bladder ("Pujifang"), fish bladder, 縼縼 gum ("Compendium of Compendium of Materia Medica"), fish belly ("Medical Compendium of Materia Medica").
The source is the swim bladder of the fish of the family of Shishuidae, such as big yellowtail, small yellowtail, or sturgeon, such as Chinese sturgeon and locust fish. Animal form details "stone head fish", "sturgeon", "fish" article.
Collection of swim bladder, cut open, remove blood vessels and mucous membranes, washed, flattened, sun-dried; or washed and fresh. After melting, the frozen gel is condensed and called "swim bladder gel".
The dried swim bladder of the herbs is mostly pressed into oblong slices, light yellow, horny, slightly glossy. The swim bladder of yellow fish is small, and the swim bladder of sturgeon and locust fish is large, with two pendant bands. The texture is tough, not easy to tear, cracked at the fibrous; easy to swell into the water, boiling is almost completely dissolved, thick solution cooled gel into jelly glue, sticky and strong. Gas slightly fishy, light flavor. Commodities collectively known as fish maw. Sturgeon, sturgeon swim bladder known as "yellow lip belly" or "yellow sturgeon gum". There are cut into lines called "line fish glue".
Produced in Zhejiang, Fujian, Shanghai and other places.
Concocted swim bladder: baked soft, cut into sections, dry. Clam powder fried fish glue: first clam powder put in the pan fried hot, then cut off the fish glue into the fire, stir-fried to the degree of loose bubble, remove the sieve of clam powder that is made. (Each 10 pounds of fish glue, with 2.5 pounds of clam powder)
"Ben Jing Feng Yuan": "Where the swim bladder glue into the pill, cut into small pieces, clam powder fried into beads, can be ground. The honey is mixed with honey, and it should be cooled and used, and it should not be pounded, and it will be sticky and hard to make pills."
Taste sweet, flat.
① "Sea Drugs Materia Medica": "non-toxic."
② "Compendium": "Sweet, flat, non-toxic."" Swimbladder gum, sweet and salty, flat, non-toxic."
③ "New Series of Materia Medica": "Sweet flavor, temperature."
Attributed to "New Edition of the Materia Medica": "Into the kidney."
Functions and Indications: Tonifying the kidney, nourishing the essence, nourishing the sinews, stopping bleeding, dispersing blood stasis, and reducing swelling. It is used to treat kidney deficiency and spermatorrhea, postpartum wind spasm, tetanus, hematemesis, hematochezia, traumatic bleeding and hemorrhoids.
① "Gleanings of Materia Medica": "the main bamboo wood into the flesh for a long time, take the white compress sores on the four sides of the meat rot that is out of the thorns."
② "Sea Drugs Materia Medica": "the main eclipse sores, pubic sores, hemorrhoids, and burned ash with."
③ "Drinking Meals are about to be": "and wine to take, eliminate tetanus."
④ "Compendium": "swim bladder, stop folding injury blood out of more than; swim bladder gel, burned to save the sex, the treatment of women's difficult labor, postpartum wind convulsions, tetanus spasm, to stop vomiting blood, blood stasis, eliminating the swelling of the venom."
⑤ "New Series of Materia Medica": "tonifying lean blood."
⑥ "Materia Medica Seeking Origin": "Nourish the tendons and veins, set the hands to fight, and fix the essence."
Usage and dosage for internal use: decoction, 3 to 5 money; boiled cream or powdered into pills, powder. External use: dissolve and apply.
Contraindications: Not to be taken if the stomach is dull and phlegmatic.
Selection ① treatment of kidney water deficiency, yin deficiency and blood deficiency: fish swim bladder one catty (bran surface fried char, ground to remove the coarse powder, and then fried and then ground), tribulus terrestris four taels, Angelica sinensis four taels (washed in wine), Cistanches four taels (remove the scales of the armour, washed in wine), Lotus root, cuscuta seed four taels (boiled in wine). Pill with honey, as big as a tung seed. Take two or three qian per serving. ("Diocesan prescription" swim bladder pills)
② treatment of kidney deficiency, not solid, dream slippery ejaculation: yellow fish swim bladder gel one catty (chopped, clam powder fried into beads, and then mixed with the milk crisp fried), Shayuan Ling quinoa eight two (horse milk soaked overnight, steam a cone of incense in the soup, roasted or sun-dried), Schisandra chinensis two two. Research for fine powder, refining white honey in the addition of old wine and then boil, wait for the honey will be cold for the pill, such as mung bean size. Take eight or ninety pills each time, and send them down with warm wine or salt soup on an empty stomach. ("Certificate of Treatment" Polyjuice Pill)
③ treatment of post-partum tapping straight, is the wind into the child's organs, and tetanus with: swim bladder glue one or two. To snail powder fried coke, remove the powder, for the end. The first thing you need to do is to take three servings, and then decoct Cicada Sugar Soup. ("Jing effect production treasure")
④ treatment of tetanus, mouth, straight: fish glue burning seven points, stay sex, research fine, into the musk a little. Each serving of two money, wine under the wine, do not drink wine, under the rice soup. ("Three Causes of Fang")
⑤ Treatment of vomiting blood: swim bladder glue eight inches long, two inches wide, roasted yellow, scraping two money. The first thing you need to do is to use thirty-five sugar cane knots and mix them down with natural juice. ("Experience Formula")
⑥ treatment of red and white collapse: fish Xuanjiao three feet, roasted yellow research powder, with chicken seeds pancakes, good wine to eat. ("Compendium")
(7) treatment of menstrual blood retrograde: fish glue (cut, fried), new sheep (burnt ash). Each serving two money, rice drink mix down. (" much can despise things ")
⑧ treatment of postpartum hemorrhagic: swim bladder glue burned to save sex, wine and children's urine to serve three, five money. ("The Years and Times")
⑨ treatment of poisons, swelling and pain, has been large and soft: swim bladder glue hot soup or vinegar fried soft, hot research and paste. ("Ren Zhai Direct Guide Fang")
⑩ treatment of eight head wind: swim bladder burning sex, for the end. The fish swim bladder is burnt and stored as a mince, and then served with onion and wine for three coins. ("Compendium")
(11) the treatment of epilepsy: swim bladder glue (slightly roasted, hang powder fried yellow), soap alum (fried yellow) each one or two, vermilion sand three money. *** for the end. Take three coins per serving, two servings under hot wine. ("Song-nyong-nyong Zunsheng" swim bladder wind scattered)
(12) treatment of esophageal cancer, stomach cancer: swim bladder, fried in sesame oil, crushed. Take 5 grams each time, three times a day. (Inner Mongolia "Chinese herbal medicine new medical method information selection")
Famous experts ① "Ben Jing Feng Yuan": "swim bladder gel with Sha Yuan Tribulus Terrestris name poly essence pill, for the essence of the important medicine. Dan Fang and a taste of fried research, sugar, daily service of one money dagger, the most good hemorrhoids, hemorrhoids after a long time from the withered. Burning ash, post-partum wind convulsions, tetanus spasm, take it to nourish and glorify the meridians, and the virtual wind from the rest."
② "New Series of Materia Medica": "swim bladder glue thick, into the kidney to replenish the essence, fear of greasy and stagnant, add ginseng to gas line in which the essence of a more beneficial life, without the disadvantages of the glue also."
Early fish evolution
In the five major categories of vertebrates, fish is the lowest, the earliest time on Earth. We are all familiar with living fish, but we are more rusty on early fish in geological history and how they evolved into living fish. Now let's take a step back in time.
The earliest known fish fossils, found in the late Cambrian strata about 500 million years ago, are only a few scattered scales, failing to give us an outline of the fish body. It was not until the late Silurian and Devonian periods, between 400 million and 350 million years ago, that a large number of fish fossils were discovered. These fish fossils, some of which are quite different from each other in terms of structural features, indicate that multiple types of fish existed at that time. In all likelihood, they had already gone their separate ways before the fossil record was available, and had traveled a considerable distance on their own evolutionary paths.
The earliest fish were jawless. As the name suggests, they did not yet have upper and lower jaws, but only a funnel-shaped mouth located at the front of the body. This kind of mouth, can not actively feed, only rely on the current to bring tiny organisms into the mouth. Further they have no ventral fins, but have a membranous exoskeleton that wraps around the outside of the body. This is why jawless fish are also known as armored fish. The existence of this exoskeleton has given rise to a debate among scholars as to whether cartilage or hard bone came first. In the vertebrate embryogenesis