Ammonia is steadily released into the water through the excreta and gills of fish as a product of their metabolism, but must be filtered out of the water since higher concentrations of ammonia (commonly between 0.5 and 1 ppm) Ammonia can be converted into safer nitrogenous compounds through combined healthy populations of 2 types of bacteria: Nitrosomonas which convert ammonia into nitrites, and Nitrobacter which then convert nitrites into nitrates.
While nitrite is still harmful to fish due to its ability to create metehemoglobine, which cannot bind oxygen, by attaching to hemoglobin, nitrates are able to be tolerated at high levels by fish.
Aquatic effluents, resulting from uneaten feed or raising animals like fish, accumulate in water due to the closed-system recirculation of most aquaculture systems.
The effluent-rich water becomes toxic to the aquatic animal in high concentrations but this contains nutrients essential for plant growth.
Other species of vegetables that grow well in an aquaponic system include watercress, basil, coriander, parsley, lemongrass, sage, beans, peas, kohlrabi, taro, radishes, strawberries, melons, onions, turnips, parsnips, sweet potato, cauliflower, cabbage, broccoli, and eggplant as well as the choys that are used for stir fries.
There is a branch of aquaponics using saltwater fish, called saltwater aquaponics.
A setup based on the deep water system developed at the University of Virgin Islands was built in a greenhouse at Brooks, Alberta where Dr.
Nick Savidov and colleagues researched aquaponics from a background of plant science.
Canada saw a rise in aquaponics setups throughout the ’90s, predominantly as commercial installations raising high-value crops such as trout and lettuce.
Inspired by the successes of the New Alchemy Institute, and the reciprocating aquaponics techniques developed by Dr.
Mark Mc Murtry et al., other institutes soon followed suit. James Rakocy and his colleagues at the University of the Virgin Islands researched and developed the use of deep water culture hydroponic grow beds in a large-scale aquaponics system.
The team made findings on rapid root growth in aquaponics systems and on closing the solid-waste loop, and found that owing to certain advantages in the system over traditional aquaculture, the system can run well at a low p H level, which is favoured by plants but not fish. An electric pump moves nutrient-rich water from the fish tank through a solids filter to remove particles the plants above cannot absorb.
The water then provides nutrients for the plants and is cleansed before returning to the fish tank below.