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 swim bladder, the gas-filled sac that helps most other fish remain buoyant.

它们还必须不停地游动以避免下沉，因为大多数鱼基本上或完全失去了鱼鳔，这个充满气体的囊帮助大多数其他鱼保持浮力。

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Indeed, the world's 37 species of seahorse are fish, breathing through gills and using a swim bladder to control their buoyancy.

事实上，世界上有37种海马是鱼，它们通过鳃呼吸，用鱼鳔来控制浮力。

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