Rob Torcellini bought a $700 greenhouse kit to grow more vegetables in his backyard. Then he added fish to get rid of a mosquito problem and before long he was a committed aquaponic gardener.

Now his 10 by 12 foot greenhouse is filled with not only vegetables, but fish. And the best part is: the poo from that fish is what fertilizes his garden.

Fish poo as fertilizer

“The fish excrete ammonia through their gils as their waste and that ammonia travels in the water and gets pumped into the growbeds,” explains Torcellini, “and there’s a naturally occurring bacteria that converts the ammonia into nitrites and then the nitrates and then the nitrates are absorbed by the plants as a fertilizer. So it’s a whole natural process that breaks it down.”

You don’t have to understand the chemistry to grow this way. There are hundreds of Americans, and thousands of Australians (it’s popular in this drought-prone country because aquaponics uses 80-90% less water than traditional agriculture), who are growing fish in a symbiotic environment with their vegetables.

Aquaculture + hydroponics

Aquaponics combines fish farming (aquaculture) with the practice of raising plants in water (hydroponics). It’s organic by definition: instead of using chemical fertilizers, plants are fertilized by the fish poo (and pesticides/herbicides can’t be introduced to kill pests because they could harm the fish).

Since the plants don’t need dirt, aquaponics allows gardeners to produce more food in less space. And in addition to the vegetables they can grow, most aquaponics gardeners cultivate edible fish as well.

Backyard fish farming

The most popular choice of fish is tilapia because it’s breeds well, grows fast and can survive in fluctuating water conditions (i.e. changes in temperature, pH and oxygen). Though tilapia are a warm water fish so for people in colder climates- like Torcellini who lives in Eastford, Connecticutt-, it’s not a great option.

Torcellini is currently farming goldfish and some koi, but he explains that if he wanted to grow edible fish, he could switch to a cold water fish like trout or perch.

In this video, Rob shows us the aquaponics greenhouse in his backyard, that he built mostly from scavenged parts, as well as his DIY indoor system where he’s growing lettuce under a grow light. He also shows us how he built his systems and talks about how most aquaponics farmers are do-it-yourself types.