The Ostariophysi are a group of real bony fish (Teleostei). Their common feature is Weber's apparatus , a connection between the inner ear (labyrinth) and the swim bladder (Greek physē ) consisting of a series of bones (large ostaria ) on both sides of the spine . This serves to improve hearing, the swim bladder acts as a soundboard . The bones evolved from the first four vertebrae.
Another common feature is an alarm pheromone , which is secreted from special cells of the epidermis in the event of injuries and warns members of the same species of danger ( deterrent ).
With well over 6000 species, two thirds of all freshwater fish belong to the Ostariophysi . Only a few Ostariophysi live in the sea (with normal salinity: some catfish ).