Aquaponics
Aquaponics is a sustainable way of producing food by simultaneously growing vegetable/herbs and fish (or prawns). The fish are fed by the owner, but also feed on the bacteria that multiply in the substrate that the plants grow in. In turn, the waste from the fishes are circulated into the root system of the crops, which absorb it as a food source.
The video below explains it better.
The video below explains it better.