It is the general name of Shark Order (sole shark). Shark knowledge: The English names of sharks are Chordata, Vertebrates and Chondrichthyes. According to the Lars classification system of 197 1 year, sharks are divided into eight orders, which are regarded by some people as the fiercest animals in the ocean. Whale sharks feed on small marine life, similar to baleen whales. Because foods have some similarities, they look very similar to baleen whales after a long biological evolution. This is the so-called "convergent evolution". So the name "whale shark" is natural. Of course, whale shark is the largest shark in existence and the largest known fish. Sharks Sharks are characterized by being hard, muscular and spindle-shaped to varying degrees. The nose and mouth are pointed according to different species, such as mako shark and great white shark; There are also big and round ones, such as tiger sharks and wide-headed tiger sharks. The vertical tail (caudal fin) is generally crescent-shaped, and the upper part of most species caudal fin is much larger than the lower part. When sharks swim, they mainly rely on the serpentine movement of their bodies and the paddle swing of their tail fins. Stability and control are mainly based on the use of more or less vertical dorsal fins and horizontal pectoral fins. Most sharks don't retreat, they are easily entangled in obstacles such as gill nets, and once they are entangled, it is difficult to extricate themselves. Sharks don't have swim bladders, so the proportion of such animals is mainly determined by the amount of oil stored in the liver. Sharks are slightly denser than water, that is, if they don't swim actively, they will sink to the bottom of the sea. They swim very fast, but they can only keep high speed for a short time. Sharks have 5-7 gill slits on each side (unlike carp we usually buy in the market, there is a pair of gill covers to protect the gills). When swimming, seawater is inhaled through the half-open mouth and flows out from the gills for gas exchange. It does look terrible for sharks to swim with their mouths open, but can you not let others breathe? Some shark species can stop at the bottom of the sea to breathe. Research on Sharks Marine biologists at the University of Hawaii in the United States say they have obtained first-hand evidence that sharks can detect changes in the earth's magnetic field. This discovery provides a new example to prove that marine fish have a "compass" system to guide them to identify their directions. This latest research result was published in the Proceedings of the Royal Academy of Sciences. Carl Meyer, a marine biologist at the University of Hawaii, and his colleagues designed and planned this experiment. They trained six sandbar sharks and a hammerhead shark in an artificial magnetic field. This artificial magnetic field environment is a water tank with a diameter of 7 meters, surrounded by a copper cable. Whenever food is put into the water tank, the cable switch will be turned on to simulate the magnetic field environment. After six weeks of training, no matter when the cable TV switch is turned on, sharks will still gather in the usual feeding area even if there is no food in the sink. The fact of this reaction proves that they feel the existence of magnetic field. Before scientists conducted this experiment, some strange habits of sharks had led scientists to speculate that sharks might have this special ability. Tiger sharks and blue sharks can swim straight in the ocean for a long distance, which is impossible if they only rely on their sense of smell. Hammerhead sharks often gather near undersea mountains, where the earth's magnetic field changes. Scientists' next research is to find out how sharks can distinguish the earth's magnetic field and how sensitive they are to magnetic field induction. Not long ago, scientists knew that other animals also have the ability to recognize magnetic fields. Researchers at the University of North Carolina in the United States have proved through experiments that pigeons have tiny magnetic particles on their upper beaks, which can help pigeons complete long-distance flights. In the past 20 years, the shark fin trade in the market has become more and more popular, and millions of sharks are slaughtered every year. At least 10 species of sharks have been added to IUCN's "2004 Endangered Species List", including great white sharks, New England sticklebacks and Gulf of Mexico white sharks. An important reason why sharks are killed in large numbers is that people accept the false propaganda that shark cartilage (including the famous "shark fin") can fight cancer. According to a recent report by Russian News Network, Gary ostrander, a professor of biology and comparative medicine at Johns Hopkins University in the United States, pointed out in a newly published research report that sharks can also suffer from cancer. At the same time, eating shark cartilage has no obvious effect on treating cancer. Professor Gary ostrander believes that the rise of shark cartilage eating habits is just a victory of "pseudoscience" through marketing. He said that eating shark cartilage is not only not conducive to treating patients, but also will cause great harm to shark population-patients often blindly believe in the efficacy of these cartilage, refuse other treatment methods, and wanton killing activities lead to a rapid decline in the number of sharks. Sharks were once regarded as insulators of cancer, and their cartilage powder was promoted as a good medicine for treating cancer. As early as 1983, Anne Lee and Robert Langer, two biochemists from Massachusetts Institute of Technology, published an article in the famous American journal Science, saying that squalene in shark cartilage can block the angiogenesis of cancer cells and proved that it can inhibit the growth of cancer cells. 1993 "60 Minutes" on CBS TV invited Dr. William Lance, the author of "Sharks Don't Get Cancer", to discuss the research results that shark cartilage can fight cancer. Several patients with advanced cancer said in the program that after taking shark cartilage capsules for several weeks, they felt their symptoms relieved. Since then, shark cartilage has been widely circulated through books, articles, websites and vendors. Subsequently, the pharmaceutical factory launched a pill made of shark connective tissue in the market, claiming that this shark pill is a "good medicine for treating cancer", creating a market with annual sales of shark cartilage products exceeding 50 million US dollars, and the largest shark cartilage manufacturer is Dr. William's son. From 65438 to 0994, the US Food and Drug Administration (FDA) officially approved the use of shark cartilage products to prevent and treat cancer. As a result, shark cartilage products have become a hot spot in the health care products market, affecting the whole world. In China, shark cartilage products and restaurants selling shark soup were once very popular. In the late 1990s, the anti-cancer theory of shark cartilage powder spread to China. At that time, there were two kinds of shark cartilage products on the market: one was shark cartilage bone powder after physical processing, and the other was active extract extracted by chemical method. In addition to vigorously promoting the number of "effective ingredients" in anti-cancer, the former claims that the fineness of bone meal grinding is exquisite, and the fineness must be above 200 meshes before it can be absorbed by the human body. The finer the better. It is said that the fineness of some products in the United States has reached 300 meshes, which greatly improves the human body's absorption of active egg white, the effective component of bone meal. The latter said that two kinds of angiogenesis inhibitors with anti-tumor function were purified from very complex shark cartilage tissue, and a series of anti-cancer drugs such as shark chondroitin capsules and shark cartilage powder were made according to these components. This medicine used to sell well in China market. Because sharks have this unique anti-cancer function, there has been a "craze" for eating sharks in society, especially in restaurants in Hong Kong and Guangzhou, where shark cartilage is boiled and sold as soup, which is called "shark cartilage old fire soup" with various varieties. These restaurants claim that this soup not only has anti-cancer effects, but also has the functions of beauty beauty, strengthening bones and muscles and nourishing the spleen and stomach. As a result, people eat it in an endless stream. Recent research shows that sharks themselves can get cancer. Recent studies have shown that sharks themselves may suffer from a variety of cancer diseases, including cancer of cartilage tissue. In his research report, Professor Gary ostrander cited 40 examples of sharks suffering from tumors, which overturned the previous statement that sharks have no cancer. American scientist John Hasbage also pointed out at the 9 1 annual meeting of the American Anti-Cancer Association that sharks can get cancer. Hasbage, a scholar working at the National Cancer Institute in the United States, discovered 50 kinds of cancers of cartilaginous fish, 23 of which came from various sharks, and some of them grew directly in cartilage. It is worth noting that Dr. William Lance, the author of Shark Can't Get Cancer (he can be called the father of shark therapy), recently admitted that sharks do get cancer, and admitted to the outside world that his conclusion that shark cartilage extract can treat cancer is only based on extremely limited experimental results. Clinical experiments have proved that shark cartilage powder has no cancer treatment effect. In fact, so far, the clinical experiments of shark cartilage powder's anticancer effect have been proved to be ineffective. Danish scholars reported at the European breast cancer conference that they found that women who took so-called "alternative anticancer drugs" made of shark cartilage did not benefit from this drug. Danish researchers tested 17 patients with advanced breast cancer with shark cartilage extract, and gave 17 patients a considerable number of shark pills, taking 24 tablets a day. After three months, among 17 patients, 15 people's cancer continued to deteriorate. Another patient showed signs of improvement at first, but later a new tumor was found in his brain. In addition, in another clinical experiment, more than 50 patients with breast cancer, lung cancer, prostate cancer, colorectal cancer and so on. After using the purified shark cartilage protein, there is no obvious improvement. Moreover, according to the research of the National Institutes of Health, protein molecules in shark cartilage are too large to be easily absorbed by the intestine, and even if absorbed, they will be decomposed and destroyed. Health food named shark cartilage has no curative effect on cancer. Not long ago, the US Food and Drug Administration and the Inspection Bureau filed a lawsuit against William and his son's laboratory and factory, demanding that the false advertisement that shark cartilage products can resist cancer be stopped. The US Federal Trade Commission also ruled that any false propaganda of shark cartilage products is prohibited unless there is relevant scientific evidence to prove it. William Lance Laboratory has to pay a judgment fee of $6,543.8+0,000, of which $450,000 will be given to the National Cancer Center and William Lance Laboratory to jointly conduct large-scale clinical trials on shark cartilage to find out the truth. Scientists believe that all kinds of healthy foods named shark cartilage have no obvious effect on cancer. Anti-cancer of shark fin is a new version of the unscientific saying "what you eat supplements what you eat". To take a step back, even if sharks don't have some kind of cancer that humans suffer from, it can't be concluded that shark products can treat human cancer. For example, cats and horses don't get prostate cancer. Studies have shown that even eating the prostate of cats and horses cannot prevent prostate cancer. And sharks can cause cancer, so consumers who try to eat expensive shark bone powder to fight cancer should think twice. Medical experts believe that most healthy foods advertised as "anti-cancer" only sell "hope". What consumers really need to look forward to is the progress of science and technology, not the superstition of commercial advertisements. In a sense, sharks are all teeth, and the scales covered on their bodies are similar to teeth, which can be called skin teeth. Sharks have hundreds of teeth and can move, so sharks don't have to worry about not having enough teeth, so they are very aggressive. Before sharks go to sleep, it is generally believed that sharks never sleep. According to the Florida Museum of Natural History, whitetip sharks, tiger sharks and great white sharks actually sleep. They sleep during the day and come out at night. Other species, such as nurse sharks, force water through gills through stomata, providing stable oxygen-rich water so that they can breathe when they are still. The central test signal generator, the organ that dominates swimming, is located in the spinal cord, allowing sharks to swim unconsciously. But because the fish has no eyelids, it is impossible to judge whether the shark is sleeping. Great white shark is by far the most powerful shark in the ocean, which is dominated by its powerful teeth. Like most animals, sharks reproduce sexually. The mating behavior of sharks is very complicated, and the routine procedures of different kinds of male and female sharks before mating are also very different. There are some behavior patterns, such as traveling together, biting people and changing colors. Sharks such as basking sharks adopt a complex social behavior, and the purpose of this behavior is still unclear. The oocysts of Echinococcus brachypomum are often called "Mermaid's purse". Male and female sharks successfully mate, and after the eggs in the female shark are fertilized, the fertilized eggs of this shark will continue to develop in one of the following three ways: the shark that lays eggs has a thick egg sheath, which can be attached to rocks or seaweed to resist predators. After these eggs hatch in a few days or weeks, the sharks will leave the young sharks and let them live independently. Most egg sheaths are wide and rectangular, and the "mermaid wallets" laid by some horned sharks are often washed to the beach. Sharks give birth to cubs, which are nourished in the uterus of female sharks through the placenta or a secretion called uterine fluid. Viviparous ensures that the young can reproduce well during their growth, so they can survive in the harsh ocean immediately after birth. Sharks also maintain embryos in their bodies and then give birth to live cubs, but they can't provide any direct nutrition for their offspring. On the contrary, developing sharks live on the yolk sac of eggs. Some kinds of sharks, such as mako, use the "egg-eating" method, that is, the mother shark lays a string of unfertilized eggs and is eaten by the growing embryo. 1. Oviposition: generally adopted by large sharks. Shark's eggs are large and there is no shortage of nutrients. The discharged egg is wrapped in a flat sheath, which is placed around the egg when it passes through the fallopian tube. The sheath will harden when it enters the water. Every corner of the sheath has a short and hollow corner, through which seawater can enter and let the eggs get oxygen. The number of ovulation is limited. Eggs are bag-shaped or spiral, and are fixed in coral reefs, marine benthos or cracks after spawning. The empty oocysts of spiny mackerel washed up on the coast are nicknamed "mermaid's wallet". 2. viviparous (non-placental viviparous): fertilized eggs develop in the uterus, eggs discharged from yolk sacs or ovaries are the source of nutrition, and placentas are not formed in the uterus. Except for whale sharks, which can produce more than 300 whales at a time, most of them are from ten tail, and the least is fox sharks (long-tailed sharks), which only produce two whales at a time. 3. Viviparous (placenta viviparous): The fertilized egg with stratum corneum develops in the uterus, and the nutrients needed for growth are obtained from the yolk sac placenta, which is not produced until the young shark is almost completely formed, and the number is ten tail at a time. Most sharks in the ocean are viviparous. Most sharks breed according to the season every year, and some big sharks breed every other year. Most sharks are pregnant for 8-9 months, and the pregnancy of white-spotted sharks is as high as 24 months. Generally speaking, big sharks produce more small sharks at a time, while small sharks are the opposite. The growth of sharks is also extremely slow, and sexual maturity is only considered at the age of 5- 10. There are many kinds of sharks, including at least 350 species in the world's oceans. Sharks, known as mako sharks, mako sharks and sand fish in ancient times, are giants in the ocean, so they are called "wolves in the sea". Sharks eat meat so fiercely that even whales, the "king of the sea", have to avoid it. Its greedy and ferocious nature left a terrible image for people when feeding bait. Therefore, when it comes to sharks, people often feel scared when they say it. Sharks are better at catching food than tigers. They can make full use of their unique sense of smell to detect the direction and position of food, while tigers only use their eyes and nose to find food. Strange sense of smell According to fossil investigation and scientists' calculations, sharks lived on the ground for about 65.438+0.8 billion years. They existed as early as 300 million years ago, and their appearance has not changed much so far, which shows that they have strong viability. However, its character is extremely fierce. No wonder people have great prejudice against it and think it is so primitive and stupid. In fact, sharks not only have a highly developed brain, but also can store information in the center of the brain with the help of electromagnetic fields and send information directly to the motor nervous system. And rely on a keen sense of smell to maintain all life activities. So the sense of smell is more important and mysterious to sharks. Sharks are particularly sensitive to the smell of seawater, especially to the smell of blood, low-frequency vibration or a small amount of bleeding caused by irregular swimming of injured fish, which can attract them far away, even exceeding the sense of smell of land dogs. You can smell the fishy smell of flesh and blood with the concentration of 1ppm (one in a million) in the water. Japanese scientists have found that even if only 1 g amino acid is dissolved in 1 10,000 tons of seawater, sharks can detect the smell and gather together. For example, after giving birth, a female shark can swim back to her birthplace with the smell even if she roams thousands of miles in the sea. A shark with a length of 1 meter has dense olfactory nerve endings of 4,842 square centimeters, such as a man-eating shark with a length of 5-7 meters. Its sensitive sense of smell can smell the blood of injured people and marine animals several kilometers away. More interestingly, sharks can also distinguish their children according to various smells, distinguish enemies from friends, maintain group contact, and meet male and female sharks to lay eggs and sperm. Because sharks have a keen sense of smell, they can easily smell their own fear or disgust. Sharks can also detect the smell of L- hydroxyalanine, a human secretion with a content of 80 billion in seawater. It is said that there was once a professional shark catcher. In the later shark catching, the shark never caught his hook again, but other fishermen in the same fishing ground caught more sharks instead. Why are sharks afraid of this shark catcher? According to the research of ichthyologists, shark catchers once suffered from skin diseases, so the fingerprints left on fishing rods contain this L- hydroxyalanine. When sharks smell this smell, they will naturally retreat from him, which is why they don't take the bait. Unique teeth It is known that sharks have many unique ecology in marine life. Besides a keen sense of smell, sharks rarely get sick and die. The tooth structure of sharks is another unique ecology. Anyone who is familiar with sharks knows that its teeth are like a sharp knife, which can easily bite off a cable the thickness of a finger. Such as the devil shark, has a long, pointed nose and sharp teeth. The teeth of different kinds of sharks are almost different in size, shape and function. Therefore, ichthyologists can judge which order, genus and family sharks belong to only by the shape and size of their teeth. Surprisingly, shark's teeth are not fixed in a row like other animals in the ocean, but there are 5-6 rows. Except for the outermost row of teeth, the other rows are "supine", just like the tiles on the roof. Once the outermost tooth falls off, the inner row of teeth will move forward immediately to make up for the hole position that replaces the fallen tooth. At the same time, shark's larger teeth have to be replaced by smaller ones in the process of growth. So sharks often have to change tens of thousands of teeth in their lifetime. According to statistics, a shark needs to replace more than 20,000 teeth in 10 years. Its teeth are not only strong, but also extremely sharp. For example, some sharks have sharp teeth like razors, so they can be used to cut food. Some teeth are serrated and can be used to tear food; Other teeth are flat mortar-shaped, which can be used to crush food shells and bones. It seems that Indians in North America use shark teeth as shaving tools. But the terrible thing is that when they compete for each other's food, sharks often indiscriminately, and even their own children, shark cubs, are not spared and are completely eaten; When a shark fights with other sharks due to accidental injury, the injured shark will be unlucky, and other brothers of the same clan will gang up and attack it until it is completely swallowed up; What is even more frightening is that a shark can give birth to more than 10 sharks in one fetus, and the highest number can reach more than 80. These sharks actually kill each other in their mother's womb. People once found the belly of a tiger shark on the Atlantic coast, and made an autopsy to conclude that the womb of the mother shark has become a battlefield, which is unprecedented in any animal. The reason why sharks change their teeth like this is not only related to their cruelty, but also to their different tooth shapes. Because the biting force of sharks can be said to be the most powerful of all animals in the ocean. Someone once used a metal bite device hidden in bait to measure the bite force of an 8-foot-long shark. The results show that the bite force is as high as 0/8 ton per square inch/kloc. Therefore, it is not surprising that some merchant ships recorded in their nautical diaries that their propellers were bent by sharks and their hulls were bitten by sharks. The shape of shark teeth is very strange. For example, the tooth edge of a man-eating shark is serrated and triangular; Great blue shark's teeth are big and sharp; Whale sharks are huge, but their teeth are as short as needles; Conodont shark's teeth are conical, long and sharp; The teeth of long-tailed sharks are flat and angular; The teeth of basking sharks are very small, as many as rice grains; Tiger sharks have wide mortar-shaped teeth and so on. As mentioned above, the diversity of shark teeth is closely related to its ecological feeding habits. Why are fish afraid of sharks and sharks afraid of dolphins? Fish are afraid of sharks and sharks are afraid of dolphins. Groups of dolphins joined forces to besiege sharks in an organized way, and hit them on the side with their powerful noses in turn. Because the shark's bones are soft and its ability to protect its internal organs is poor, smart dolphins seize its key points and fight hard to prevent it from having a chance to breathe until the shark's internal organs are damaged, and often sharks die quickly in panic attacks. Shark's head has a special cellular network system, which can detect current. This system is called inductance. Sharks use electric sensors to prey on prey and swim freely in the water. American researchers studied the embryos of spotted cat sharks. Through molecular tests, they found two independent genetic markers of neural crest cells in shark electroreceptors. Neural crest cells are embryonic cells that form various tissues in the early stage of embryonic development. Human neural crest cells play an important role in the formation of human facial bones and teeth. This discovery shows that neural crest cells move from the shark's brain to various areas of the head and develop into electroreceptors in the head. References:

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