Final answer:
Most fish control their buoyancy by regulating the amount of gas in their gills.
Step-by-step explanation:
True. Most fish control their buoyancy by regulating the amount of gas in their gills. All bony fishes, like the cartilaginous fishes, use gills to breathe. Water is drawn over gills that are located in chambers covered and ventilated by a protective, muscular flap called the operculum. Many bony fishes also have a swim bladder, a gas-filled organ that helps to control the buoyancy of the fish. By changing the amount of gas in the bladder, a fish can move up or down through the water column.