What is a Shark Shield?

Sharks belong to the phyllochondria of the vertebrate Chondrichthyes. They are marine, and a few species enter the freshwater. They are a group of fast-moving medium-large marine fish. ^[1]

The body has a long spindle shape. Gill fissure lateral, normal pectoral fin, does not heal with the leading edge of the kiss; dorsal position of northern fin; crooked tail type. ^[3]

Sharks are fertilized in vivo, and males have mating fin feet. ^[1]

There are 25 families in 8 orders, about 250 to 300 species, and about 130 species in China's sea areas. ^[3]

Physiologically active ingredients in shark blood

The whole sera of Caroharhinus plumbens can inhibit Lewis lung cancer inoculated in mice, and IgM antibody is the main serum immune protein. Its mechanism of action is related to direct cytotoxicity and indirect effects on the lymphatic reticuloendothelial system. Some of the IgM molecules in shark immunoglobulin have specific antigen-binding activity, while others have sites capable of binding multiple specific antigens. Antigens combine with immunoglobulin to form immune complexes, which can inhibit the response of lymphocytes to mitogenic factor stimulation. Shark plasma can inhibit the growth of Rolls sarcoma cells implanted in chickens; SphrnaLewini sharks have antitumor effects

Important food fish

Most sharks can be eaten fresh, steamed, marinated, or used as raw materials for fish sausages, fish pastes, canned fish, etc. When eating fresh, because the meat contains urea, urea can be removed with citric acid or lemon juice or tomato juice to improve the quality of the meat. In addition, shark shark fins (fins),

The shark is an ancient fish. Judging from the shark teeth and spine fragments unearthed, its fossils appeared 350-410 million years before the dinosaurs. In this long history, sharks have undergone natural selection, and some species have disappeared, and some of the more than 300 species that survive now still have some fragility, such as slow growth, slow sexual maturity, and reproduction once every two years. And the reproduction rate is extremely low. ^[1]

People talk about shark discoloration and liken sharks to "sea wolves" and "sea tyrants". Why do you say sharks are so fierce?

First, the shark body is spindle-shaped and swims fast. ^[1]

Megalodon means "big teeth" in Greek. The paleontological world currently has limited knowledge of it

shark

Yes, the megalodon shark can reach a total length of 20 meters, and the teeth bite force is unprecedented. ^[6]

"A series of fossils and ecological evidence show that Megalodon is indeed extinct. Megalodon is a cartilage fish. Like other sharks, its endoskeleton is cartilage and has a low degree of calcification. It is more difficult to form fossils except for teeth." Xiamen University Ocean Zhao Yu, a master of biology, said that humans have not found a complete megalodon shark fossil and cannot directly determine its size and shape. Therefore, the understanding of the megalodon shark size and shape is mainly carried out through its tooth fossils and living sharks. Compare to get. ^[6]

The largest megalodon is more than three times the length of the great white shark and exceeds the largest living shark, the whale shark, which is the largest shark in the world. "Zhao Yu said that because the teeth of the giant tooth shark are similar to the teeth of the great white shark, and the image of the great white shark is deeply rooted, so far, the restoration of the shape of the giant tooth shark is almost based on the template of the great white shark. ^[6]

In recent years, further studies on the morphology of megalodon sharks have shown that megalodon shark teeth are more similar to sand sharks, which are another species of rat sharks, and have closer kinship. Therefore, some scholars believe that the restoration of megalodon sharks based on the shape of sand tiger sharks may be more accurate. ^[6]

"But we haven't found any more fossils that can help restore the shape of the megalodon. As far as the current fossil evidence is concerned, we can't determine the exact shape of the megalodon." Zhao Yu said that the megalodon can indeed look like a movie The same bite killed the whale. Based on the bite force data of the great white shark, the researchers speculated that the maximum bite force of the giant tooth shark can reach 1.8 tons. "Such a huge bite force combined with the megacephalic shark's maximum mouth size of 2 meters, coupled with the shark biting and cutting behavior after the bite is enough, is a fatal blow." ^[6]

"Like all sharks, megalodon's teeth are replaced and lost for life. However, the megadontodon shark teeth collected by people were formed 2.6 million years ago. It can be speculated that megadon sharks became extinct 2.6 million years ago. Zhao Yu said that the study of the distribution of megalodon sharks showed that it prefers warm tropical and subtropical waters, and requires shallow waters as nursery grounds, so it is unlikely to migrate to cold, barren deep seas, and complete the entire life history in deep sea environments. . ^[6]

As a fierce hunter, Megalodon has a large amount of activity and a large energy consumption. It must eat nearly 2 tons of food every day to survive. Obviously, once food is scarce, the fragile side of life is exposed. "The megalodon shark is a huge predator with the highest trophic level. In theory, the food web structure in the current marine ecosystem cannot support the survival of such a large predator." Zhao Yu said, The claim that megalodon still lives somewhere today is untenable. ^[6]

Fossil evidence suggests that Megalodon was extinct about 2.6 million years ago, which coincides with the start of the last ice age. Therefore, some people think that megalodon sharks have become extinct because they cannot adapt to the sudden drop in sea temperature. ^[6]

A 2016 study by researchers at the University of Zurich showed that the extinction of megalodon sharks is not directly related to changes in seawater temperature. The study points out that biological factors are an important cause of megalodon shark extinction. The decline of megalodon shark populations is accompanied by the diversity of cetaceans The decline in sexuality, and the emergence of other large predatory creatures such as predatory cetaceans and great white sharks, may lead to the extinction of such prehistoric giants due to food shortages and increased predation competition. ^[6]