Weberian apparatus
A chain of small bones linking the swim bladder to the inner ear, which gives carps, catfish and tetras sharp hearing.
Also: Weberian ossicles
The Weberian apparatus is a set of small bones, reshaped from the first few vertebrae, that connects the swim bladder to the inner ear. The swim bladder picks up sound waves in the water, and the bones pass the vibrations to the ear, a little like the bones of the human middle ear. It is the mark of a huge group called the Otophysi, which includes the carps and minnows, catfishes, characins such as tetras and piranhas, and the knifefishes. Together they make up about two thirds of all freshwater fish species.