Final answer:
The swim bladder in fish is a gas-filled organ derived from the gut that helps control buoyancy. It is found in many bony fishes, but not all. Some fish may not have swim bladders due to evolutionary adaptations or different methods of buoyancy control.
Step-by-step explanation:
The swim bladder in fish has nothing to do with the actual bladder. It is a gas-filled organ derived from the gut that helps control the buoyancy of the fish. It is found in many bony fishes but not all. The gases in the swim bladder are exchanged directly with the blood in most bony fish. Some fish may not have swim bladders due to evolutionary adaptations or different methods of controlling their buoyancy.