It’s a cycle known as aquaponics, which uses dual-tanked plant-and-fish habitats to create a symbiotic environment and a sustainable system that mimics the natural world. One tank holds the fish; the other, the plants. A pump flows water between the two, aerating the water in the process. Along with hydroponics — a similar idea that focuses solely on raising vegetation — it’s a creating an alternative to traditional in-soil farming.