Aquaculture production is in full expansion and development worldwide. The demand for seafood products is increasing while aquaculture resources are maintained. Many of the species that have been fished up to now have reached their maximum production potential. As a result, it will not be possible to sustain the supply of fish and seafood in the short term. Aquaculture recirculation systems appears as a possible solution, promoting a sustainable aquaculture.

Traditional aquaculture requires a large amount of water and the acquisition of significant amounts of land. In Latin American countries, water is a limited resource due to factors such as population growth, pollution, and droughts, among others.

According to FAO reports, the main points that need to be addressed in aquaculture production are the problems of the lack of appropriate technology and financial resources, as well as the reduction of environmental impact and diseases in aquaculture production.

Advantages of recirculation systems

Aquaculture production that implements recirculation systems is a culture alternative, which allows the reuse of water by treating it physically, chemically and biologically, in order to use less than 10% of the water required in a conventional culture.

This type of recirculation system guarantees an adequate environment to promote the growth of our aquatic organisms and the efficient control of the physical-chemical parameters of the water. Furthermore, it is presented as a solution to reduce the environmental impact and allow greater control of diseases, promoting a sustainable aquaculture.

Aquaculture has shown to have sufficient potential to contribute to the production of these products, meeting the demand of the population. Aquaculture production systems based on water recirculation systemsare an excellent alternative in regions where water and land for production are scarce.

A recirculation system allows us to maintain an adequate water quality for the maintenance of our crops, this through a series of treatments of the pond water. This, in addition to giving our aquatic organisms an adequate welfare allows us to have a significant water savings.

In aquaculture, the physical-chemical parameters of the water are fundamental elements to carry out a good practice and it is precisely through a recirculation system that we can provide a stable culture medium through processes such as filtration, control of parameters such as temperature, oxygenation, levels of nitrates and nitrites, pH, among others.

Image2: Filter system

Components of recirculation systems

In an ideal recirculation system, we must keep our fish under a good diet and with an adequate water quality, maintaining their welfare to the maximum and promoting their growth.

The main points to consider when planning recirculation systems are the following:

• Elimination of solids: we must take into account that for every kilogram of food we provide to our fish, 250 g of solids will be generated, which we must eliminate by means of tools such as band filters or foamers.
• Elimination of ammonia: this is achieved by means of a biofilter, which can be of the submerged, percolation or rotary type. In general, they are simple deposits that contain some type of material to obtain colonies of nitrifying bacteria. Sometimes sacks containing porous stones can be used to facilitate the proliferation of specific bacteria for the inactivation of nitrites and nitrates.
• Oxygen supply: the supply of oxygen in the system must be guaranteed, since for every kilogram of food, an approximate supply of 500 g of oxygen must be made for the fish and for the bacteria that help us with the detoxification processes of the system, they work under an aerobic scheme, so they require a significant amount of oxygen. In addition, we must also consider the oxygen requirement in the nocturnal photosynthesis of the plants and algae that form in the pond.
• Elimination of COâ‚‚: we must consider that for every kilogram of food provided, 0.7 kilograms of COâ‚‚ will be generated, which we must eliminate by means of degassing columns or by a more practical and economic method, aeration.
• pH control: the increase of the concentrations of COâ‚‚ in the water favors an acid pH and on the other hand the bacteria require carbon to grow so we will have to take care of the alkaline reserve; so for each kilogram of food 200 grams of sodium bicarbonate will be added to the system.
• Disinfection: Ideally, ultra-violet light lamps or ozonation systems should be used to disinfect the system.
• Temperature: the recirculation systems allows the water temperature to be controlled, allowing a stable temperature to be maintained throughout the year. In addition, the temperature control together with the lighting control allow, among other things, to simulate the environmental conditions of laying.

Advantages of recirculation systems

With the above we can say that this type of system has several advantages, such as:

• Reduction of land and water use: one of the current problems is the reduction of land for production and the growing lack of water in most parts of the world, so making its use more efficient by means of a recirculation system is vital for aquaculture production.
• Reduction of energy costs.
• Complete control of water parameters.
• Reduction of organic waste from crops.
• Biosecurity: improving water conditions through a recirculation system minimizes the risks of disease transmission within the crop or zoonotic diseases.
• Recirculation systems promote a sustainable aquaculture.

The implementation of recirculation systems is proposed as a tool for the promotion of aquaculture at any scale, contributing significantly to food production in areas where there is still a high degree of marginalization, thus improving the economic condition of those involved, raising their quality of life standards and offering in the local market a fresh product without risk of contamination.