Aquaponics is the process of growing both edible plants and fish in the same system. This system may be a closed loop in which all the water is treated and recycled, or it may be a more open, linear system where water enters the local ecosystem again instead. The name aquaponics is a combination of the terms hydroponics and aquaculture. Aquaculture refers to growing fish in an enclosed tank or pond system, while hydroponics involves growing crops without soil and in some kind of water-based system that delivers the necessary moisture and nutrients. When the systems were first combined in the 1980s, aquaponics was born as its own discipline.

The system begins with the fish, which produce a lot of waste as they eat and grow. Many of these waste products are useful to plants as a source of the three primary nutrients all crops need: nitrogen, potassium and phosphorous. However, just like with animal manures used for in-ground growing, the waste products of fish need further processing before the plants absorb them. Separating the waste and exposing it to open air allows high levels of ammonia to convert into the nitrates that plants can actually absorb as a nitrogen source. Bacteria are also recruited that live in the growing medium of the plants and work hard to help the roots take in enough nutrients. Because growing fish in ponds, tanks or even open waterways produces dangerously high levels of ammonia that can kill off the fish and damage other aquatic life, processing those waste products into a useful plant food helps close the loop on this potential source of pollution.

Aquaponics offers benefits over both types of traditional hydroponics and aquaculture, which will be explored later in this book. However, it still requires plenty of planning and a dedicated management to succeed. Understanding what aquaponics is not may be equally important before you start a commercial project. Aquaponics is not:

• A set-it-and-forget-it system that can completely manage itself until harvest time (although automation will likely make this possible one day).
• A guaranteed success in any market. You need either existing demand for quality crops and fish, or extensive marketing.
• An entirely closed system. Most designs require at least occasional external supplementation for certain nutritional needs of the fish and plants.