Aquaponics (/ˈækwəˈpɒnɪks/) refers to any system that combines conventional aquaculture (raising aquatic animals such as snails, fish, crayfish or prawns in tanks) with hydroponics (cultivating plants in water) in a symbiotic environment.
Any hydroponic system can be converted to aquaponics simply by replacing the reservoir with an aquarium. Be sure to read the article Convert Your Hydroponic System to an Aquaponic System for more details.