swim bladder

Meanings

1. 1
   noun

   a gas-filled internal sac present in many bony fishes, used chiefly to regulate buoyancy and maintain depth and, in some species, also involved in respiration, hearing, or sound production

   By adjusting the gas in its swim bladder, the fish held its position without swimming continuously.

A compound of swim and bladder, recorded in English from 1837. Bladder descends from Old English blædre, 'blister or bladder'; the anatomical compound compares the fish's expandable gas sac to an animal bladder and names it for its role in swimming and depth control. Air bladder and gas bladder are alternative names.

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