The diffuser is the part of the aquaponics system that releases the oxygen back into the water to make it more appealing to fish. The air stone is the part that helps to disperse the bubbles in the water. They work together to create the most efficient system. Diffusers are used to keep oxygen levels high in the aquarium by allowing air to escape through holes or slits in the tank, thus increasing the amount of dissolved oxygen in the water.
This will help to support a higher level of fish life in your system. Air stones  also make it easier for the plants to absorb nutrients from the water.