Sharks swim mainly by swinging their bodies and tail fins, so most sharks can only move forward, not backward, so they are easily entangled in human gill nets. Because sharks have no swim bladder, their specific gravity is mainly determined by the amount of oil stored in the liver. Sharks are denser than water. If they don't swim all the time, they will sink to the bottom of the sea.
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Sharks live in the ocean, and different species have different feeding habits. For example, whale sharks are marine fish and mainly feed on plankton. Species living on the seabed, such as Hana shark and tiger shark, mainly feed on benthos such as shellfish and crustaceans.
Fierce species generally live in the upper and middle ocean, feeding on all kinds of fish and other large marine animals, and a few species can even attack people. According to records, there are more than 20 kinds of sharks that can attack people actively all over the world, among which there are more than 10 species in China, such as biting sharks, hammerhead sharks and conodont sharks.
Popular Science China-"Wolf in the Sea" Sharks have a pair of "wimps".