Aquaponics -- combining aquaculture (fish growing) and hydroponics (growing plants with their roots in water). One can make it a sustainable process by watering gardens with the nutrient rich water from the pond. One can then replace the water with rain water. This both nourishes plants and provides new, oxygen rich water for fish. The hydroponic plants can add to your harvest.
Aquaponic fishtanks are sold on-line and at some pet stores. Otherwise, you can build your own aquaponic fish tank!