Final answer:
Swim bladders help bony fish maintain buoyancy by allowing them to control their position in the water without expending energy, and are distinct from the gills, which are used for breathing.
Step-by-step explanation:
Swim bladders help bony fish maintain buoyancy. These gas-filled organs, which are derived as a pouch from the gut, allow bony fish to control their buoyancy. Unlike cartilaginous fishes such as sharks and rays, which lack such structures, bony fishes use their swim bladders to move up or down through the water column by changing the amount of gas within the bladder. This adaptation is critical for maintaining their position in the water without expending energy.
While all bony fishes use gills to breathe, swim bladders are separate from the gills and are not involved in gas exchange with the surrounding water. The purpose of gills is to extract oxygen from the water, and this function is covered by the protective operculum. Therefore, the statement that swim bladders contain gills or are required for fish to exchange gases is incorrect. Furthermore, swim bladders are found in bony fish, but not in cartilaginous fish, making the suggestion that they are present in both groups inaccurate.