In order to rise in the water bony fishes fill their swim bladder with?

In order to rise in the water, bony fishes fill their swim bladder with gas. The swim bladder, also known as the air bladder, is a gas-filled sac located in the body of bony fishes that helps them control their buoyancy. When the swim bladder is filled with gas, it provides the fish with positive buoyancy, allowing them to rise in the water. When the fish needs to descend, they can release gas from the swim bladder, which causes them to lose buoyancy and sink. The fish can control the amount of gas in their swim bladder by using a special organ called the gas gland, which is located near the swim bladder. The gas gland can secrete gas into the swim bladder or absorb gas from it, depending on the fish's needs.