What adaptation do bony fish have to compensate for the density of bone?
Bony fish have a (relatively) large gas bladder located ventral to their spine. Sharks and rays have a large liver that has neutrally buoyant oils when in motion. However, the weight of their bodies and this neutrally buoyant oil will cause them to slowly sink, which is compensated for by their heterocercal tails (the lower lobe is almost always smaller than the upper lobe, the exceptions being the long and short fin makos, which are designed to move very quickly over long distances, and so need a more efficient propulsion system).
