Aquaponics or fish farming: What it is, how it works and advantages

Last updated on October 23rd, 2023 at 08:18 pm

Aquaponics is a sustainable system of simultaneous plant and fish production that combines traditional aquaculture (aquatic animal husbandry) with hydroponics (growing plants without substrate but in water with dissolved nutrients) in a symbiotic environment in which the plants benefit from the fish and vice versa.

What is aquaponics?

As mentioned above, aquaponics has two main parts: aquaculture, for raising aquatic animals, and hydroponics, for growing plants.

The aquatic wastes resulting from fish farming are accumulated in the water by the use of closed recirculation systems implemented in most aquaculture systems. Water rich in effluent and in high concentrations can be toxic to aquatic animals; however, it is a source of essential nutrients for plant growth.

Components of an aquaponic system

Aquaponics systems are usually grouped into different components or subsystems. Typical components include:

• Rearing tank: where fish are grown and fed.
• Solids removal: a unit to remove uneaten food, detached biofilm, and fine sediments.
• Bio-filter: the place where nitrification bacteria grow and convert ammonia into nitrates, so that they can be assimilated by plants.
• Hydroponic subsystems: the part of the system where plants grow by absorbing nutrients from the water.
• Sump: the lowest point of the system where water flows and is pumped back to the rearing tanks.

Fundamentals of aquaponics

Nitrification

Nitrification is the aerobic conversion of ammonia to nitrate. It is one of the most important functions in an aquaponics system, as it reduces the toxicity of the water to the fish, and allows the resulting nitrate compounds to be removed by the plants and used for their nutrition. Fish constantly release ammonia into the water as a product of their metabolism, but most of it must be filtered out since large concentrations of ammonia can kill the fish. Aquaponics takes advantage of the ability of some bacteria to convert it into other nitrogenous compounds. In this case we distinguish two types of bacteria:

• Nitrosomonas: bacteria that convert ammonia into nitrite.
• Nitrobacteria: bacteria that convert nitrites into nitrates.

In the aquaponic system, the bacteria responsible for this process form a biofilm on all solid surfaces that are in constant contact with water. The submerged roots of vegetables have a large surface area, allowing many bacteria to accumulate on them. Care of these bacterial colonies is important to regulate the complete assimilation of nitrogen. Since the nitrification process acidifies the water, the addition of non-sodium bases, such as potassium hydroxide or calcium hydroxide, is needed to neutralize the pH of the water.

Elements of an aquaponics system

An aquaponic system consists of two subsystems:

• The cultivation of plants in hydroponics, or hydroponics subsystem.
• The cultivation of fish in attached tanks, or aquaculture subsystem.

Hydroponic subsystems

Plants are grown in the same way as in conventional hydroponic systems, with their roots immersed in nutrient-filled water. This allows them to filter out ammonia that is toxic to aquatic animals and their metabolites. After the water has passed through the hydroponic subsystem, it is cleaned and oxygenated, and can return to the aquaculture vessels, forming a continuous cycle.

Most leafy greens, such as lettuce, spinach or chard, grow well in hydroponic subsystems. Other vegetable species that grow well in an aquaponics system include: beans, radishes, strawberries, onions and aromatic herbs.

Freshwater fish are the most commonly aquatic animals raised by aquaponics, although crayfish and shrimp can also be raised. In practice, tilapia is the most popular fish in projects for food consumption, although barramundi, silver perch, tandanus catfish (siluriformes) or jade perch are also used. For temperate climates, when there is no need to maintain water temperature, Lepomis macrochirus (bluegill) and catfish are good choices for a home system. Koi and carp (or goldfish) can also be raised if the fish are not for human consumption.

How to grow plants with fish

Aquaponic systems generally do not discharge or exchange water under normal operations, so they recirculate and reuse water very efficiently. The system relies on the relationship between animals and plants to maintain a stable aquatic environment that experiences minimal fluctuation in oxygen levels and nutrient environment. Water is added only to replenish the loss due to plant uptake and transpiration, evaporation of surface water or removal of biomass as solid waste from the system. As a result, aquaponics uses approximately 2% of the water that a conventional farm requires to irrigate the same vegetable production. This allows aquaponic crop and fish production in areas where water or fertile land is scarce.

The three main inputs to the system are: water, feed given to the aquatic animals, and electricity to pump the water between the aquaculture subsystems and the hydroponics systems.

Advantages and disadvantages of aquaponics

The advantages of aquaponic systems are:

• Reuse of water, presenting an advantage for those areas where water availability is scarce.
• Organic fertilization of plants with natural fish emulsion.
• The elimination of solid waste from intensive aquaculture.
• The reduction of arable land needed for crop production.
• Reduction of the overall environmental footprint caused by vegetable production and animal husbandry.
• The reduction of pathogens that frequently plague aquaculture production systems.

Some possible disadvantages of aquaponics are:

• The initial cost of the installation.
• The large number of ways the system can be configured tends to lead to equally varied results.
• Some aquaponic installations rely heavily on human-generated energy, technological solutions and environmental control to achieve recirculation and optimal water and water temperatures. Although if a system is designed with energy conservation in mind, using alternative energy and a reduced number of pumps while still using gravity can be very energy efficient.

That is all. I hope you have found this topic of aquaponics farming interesting, see you next time Agrohuerters! 🙂 🙂