Sharks and rays have no swim bladders . Body oils help some sharks float, but most overcome their tendency to sink by swimming actively. Some types of catfish can travel over land from pond to pond, using their front fins to push themselves along the ground. When out of the water, they release a slimy substance that covers their bodies and keeps them moist. In addition to their gills, these catfish have swim bladders that they use like lungs when they are on land.
Some fish also use their bladder as an eardrum to pick up sounds.
Others use it to amplify their own sounds.