shark
(a fish in the ocean)
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Sharks, living in the ocean, are fish in the ocean.
Sharks existed on the earth as early as 300 million years before dinosaurs appeared, and have existed on the earth for more than 500 million years. They have hardly changed in the past 100 million years. 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". Traditionally, it is thought that the content of protein in shark cartilage (that is, shark fin) is high, but this is wrong. The protein of eggs far exceeds that of shark fins. In addition, the research shows that mercury is easy to accumulate in sharks, and shark wings contain a certain amount of neurotoxin, which is potentially harmful to human body. Sharks are in danger of extinction due to a large number of killings for decades.