A couple days ago I met two lovely people, Peter and Julie, here in Sydney.  They are enthusiastic Permaculturists.  They installed an aquaponics system in their backyard.  In a large tank, they are growing fresh water perch, a native Australian fish.  The water is circulated up to

 two smaller tubs filled with small gravel (called blue metal) and has plants growing right out of the gravel including lettuce, mustard greens, celery, strawberries.  The plants are thriving on this nutrient rich water; the water is cleaned through the gravel and plants and circulated back down to the fish.  It was inspiring to see how their motivation turned into something so productive.

Aquaponics (IPA: /ˈækwəˈpɒnɪks/) is the symbiotic cultivation of plants and aquatic animals in a recirculating environment.

Aquatic animal effluent (for example fish waste) accumulates in water as a by-product of keeping them in a closed system or tank (for example a recirculating aquaculture system). The effluent-rich water becomes high in plant nutrients but this is correspondingly toxic to the aquatic animal.

Plants are grown in a way (for example a hydroponic system) that enables them to utilize the nutrient-rich water. The plants take up the nutrients, reducing or eliminating the water's toxicity for the aquatic animal.

The water, now clean, is returned to the aquatic animal environment and the cycle continues. Aquaponic systems do not discharge or exchange water. The systems rely on the natural relationship between the aquatic animals and the plants to maintain the environment. Water is only added to replace water loss from absorption by the plants, evaporation into the air, or the removal of biomass from the system.

Aquaponic systems vary in size from small indoor units to large commercial units. They can use fresh or salt water depending on the type of aquatic animal and vegetation.

See who is doing it in San Diego here.