Terme de Glossaire

This is the diverticulum of the digestive tube which forms a pocket of air in the oesophagus. An air-filled bladder which gives the fish buoyancy. Some of the fish that live on the bottom of the oceans do not have this. In some fish, it can vibrate due to muscular activity and therefore produce sound. Finally, it plays a role in the hearing ability of the fish. By the difference of density in water, it can distort itself under pressure from an external sound. This distortion creates a signal (= movements of particles) which can then be captured by the ear. It has been proved that the closer the swim bladder is located to the ear, the better the fish’s hearing. Certain fish, particularly Synodontis, have even developed Weberian ossicles, a chin of three ossicles which form a joint between the bladder and the ear, and which retransmit by the distortion of the bladder wall. A fish with Weberian ossicles can hear frequencies between 0 and 5000 hertz. A fish which does not have this apparatus will not hear above 2000 hertz.