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The Weberian apparatus is amplifies hearing in Ostariophysian fish.

This series of small bones links the swim bladder to the inner ear in Ostariophysian fish, including minnows, carp, catfishes, and characins.  When a sound wave hits the swim bladder, the vibration is transferred through the Weberian apparatus to the auditory region of the inner ear.  This action helps amplify sound and, as a result, these fish have very sensitive hearing and can hear sounds that many other fish are in capable of hearing.