Many warm-water and cold-water fish species have been adapted to aquaponics systems. The most commonly cultivated fish in aquaponics systems are tilapia, cod, trout, perch, Arctic char and bass. But out of all of these, tilapia thrives best. Tilapia are very tolerant of fluctuating water conditions, such as changes in pH, temperature, oxygen and dissolved solids. They also are in high demand -- this white-fleshed fish is frequently sold in markets and restaurants.
Which plants thrive well in aquaponics systems? That depends on the density of the fish tanks and the nutrient content of the fish waste. In general, the best plants to cultivate in an aquaponics system are leafy greens and herbs. The high-nitrogen fertilizer generated through fish waste allows plants to grow lush foliage. So, leafy plants tend to flourish in aquaponics systems. Lettuce, herbs and greens like spinach, chives, bok choy, basil, and watercress have low to medium nutritional requirements and usually do well in aquaponics systems.
Plants yielding fruit have higher nutritional requirements, and although they grow well in aquaponics systems, they need to be placed in systems that are heavily stocked and well established. Vegetables like bell peppers, cucumbers and tomatoes can be cultivated in these types of aquaponics systems. The only plants that don't seem to respond as well are root crops like potatoes and carrots. Without soil, these crops wind up misshapen, and they're hard to harvest properly.
Aside from plants and fish, the other major component of aquaponics is the water itself. That said, carefully monitoring the water's pH, which determines acidity, is of the upmost importance to ensure safe levels for the fish. Water quality testing equipment is very important to ensure that both fish and plants remain healthy. It's also important to keep an eye on dissolved oxygen, carbon dioxide, ammonia, nitrate, nitrite and chlorine. The density of the fish in the tanks, the growth rate of the fish and the amount of feed they're given can produce rapid changes in water quality, so careful monitoring is important. Although the ratio of fish tank water to hydroponic product depends on fish species, fish density, plant species and other factors, a general rule of thumb is a ratio of 1:4 tank contents to bed contents. Basically, for every one part of water and fish, you'll want to have four parts plant and bed material.
Some aquaponics systems are outfitted with biofilters, living materials that naturally filter pollutants out of water and that facilitate the conversion of ammonia and other waste products. Other systems feed fish waste directly into the hydroponic vegetable beds. Gravel in the vegetable bed acts has a bioreactor, a material that helps carry out the chemical processes of living organisms. The gravel does this by both removing dissolved solids and providing a place for the nitrifying bacteria to convert into plant nutrients.
Want to bring food production into your backyard? Read on to learn how to set up your own aquaponics system.