When small creatures swim past, they bend the hairs on the bladder, causing a flap to open.
当小生物游过时,它们会弯曲膀胱上的毛发,导致膀胱瓣打开。
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They must also keep swimming to keep from sinking, since most have largely or completely lost the swimbladder, the gas-filled sac that helps most other fish remain buoyant.