鱼类,靠鳔来进行自由沉浮,当鳔内充满空气时鱼上浮,释放空气时则下沉。鲨鱼天生没有鱼鳔,一旦停止游动,它就会像石头一样葬身海底。为了生存,鲨鱼必须不断地游动,一刻也不能停歇,哪怕睡着的时候,也得奋力游动。持续地游动,要消耗大量体力;体力,得靠大量捕食猎物来补充。在弱肉强食的海底 The fish, floating freely by the bream, float when the broom is filled with air and sink when the air is released. The shark is born with no mandarin fish, and once stopped, it will get buried like a rock. In order to survive, sharks must keep swimming and can not stop for a moment, even when asleep, have to swim hard. Continuous swimming, to consume a lot of physical strength; physical, rely on a large number of prey to supplement prey. In the law of the jungle seabed