Aquaculture is a term used to describe different methods of producing different types of fish and other aquatic species. Many aquaculture methods have been developed in different parts of the world and have been adapted to the specific environmental conditions of each region.
The main methods of cultivation in aquaculture are:
1) Floating cages in freshwater rivers and bays
2) Fish ponds
3) Recycling systems with different mechanical and biological filtration methods that deal with fish waste.
When dealing with sustainability, the main problem with aqua farming methods is the production of nitrate-rich wastewater, a byproduct of all the above-mentioned methods, forcing farmers to treat or dispose of water. Both ways are costly and are potentially causing environmental pollution.
The term hydroponics is used to describe various cultivation methods of plants without soil (vegetables, medicinal plants, flowers and even small fruit trees). The water is used as the sole medium containing all the necessary nutrients for the plant. In hydroponic systems for food production, the plants are irrigated with a solution containing the nutrients, a process known as fertilization. An organic fertilizer solution can be used but in the vast majority of commercial systems a balanced inorganic fertilizer is used that provides the nutrients, the macro and the micro elements.
Hydroponics is a much more efficient method than growing plants in the soil, since the water is constantly circulating in the closed system or, in case of micro-irrigation, in an open system. When dealing with hydroponics, the main problem is the absolute reliance on adding fertilizers to produce nutrients.
Aquaponics is a combination of two growing methods in one system: Aquaculture and Hydroponics. This combination effectively eliminates the polluting factors of each of the growth methods when standing alone as mentioned above.
Aquaponics relies on fish secretions to serve as an organic fertilizer solution for growing vegetables. In an aquaponic system, water is pumped from the fish tank to a biological filter, where the bacterial population decomposes the fish secretion into an organic fertilizer solution. The roots of the plants then absorb the nutrients from the water, effectively cleaning the water before returning to the fish tank. The bacteria are the foundation of this process. They convert the ammonia (NH3), which is the main component of the fish secretion, to nitrate (NO3, a more accessible form of nitrogen for the plants) and thus prevent the water from becoming toxic to the fish (this process of conversion from ammonia to nitrate is called nitrification).
Each aquaponic system requires a biological filtration unit to populate the bacteria and allow them to permanently convert ammonia to nitrate. Although the main products of the aqua system are fish and vegetables, it is important to remember that the aquaponic system is an ecosystem containing three organisms: fish, plants and bacteria.