Recirculating systems are among the technologies at the vanguard of aquaculture engineering. Recirculating Aquaculture Systems (RAS) allow fish to be farmed in net cages or tanks instead of open-air ponds. These systems allow high-density fish production within a breeding environment that is controllable by the operator of the facility. The filters of the recirculating system clean and recycle the water, sending it back to the tanks. New water is only added to the tanks to compensate for water lost due to splashing and evaporation, and to replace that used to remove waste materials.
The main advantages of Recirculating Aquaculture Systems are easily quantifiable. The first is that they require far less water than conventional systems. Since RAS farms recycle most of their water, they consume much less, making them particularly suitable for areas with limited water reserves.
A correctly designed and operated recirculating system requires a minimum daily water intake, enough to clean the filter residues and to replace the water lost by evaporation. This allows farms to be constructed in areas where groundwater is limited and even in urban areas where chlorine-free municipal water is used.
The second advantage of RAS systems is that they require far less surface area due to the much higher stocking density. In pond aquaculture, the stocking density can exceed 40 kg/m3 depending on the species; therefore, a recirculating system can be located in areas where large amounts of flat land (to build ponds) are not available. These facilities can also be located in areas where the land may not contain water, or in urban areas or empty facilities (warehouses) that can be converted into fish farms.
The ability to control the water temperature is the third advantage of RAS farms. Due to the reduced water requirements, the recirculating systems use little water, so the farmer can control the water temperature (and the growth rates of the fish stock) to produce certain species of fish that normally could not be raised in a given geographical area. It also allows the water temperature to be maintained at the optimal level to maximize feed conversion and ensure optimal growth. In addition, growth can take place year-round, which maximises production and allows rapid product turnover.
The fourth advantage of RAS systems related to water is quality control. By maintaining the dissolved oxygen at optimal levels, this technology ensures that fish have better feed conversion and reduced stress, resulting in improved resistance to disease, less food waste and higher growth.
Another important advantage of these types of systems is that fish farming in enclosed facilities guarantees excellent protection against adverse weather conditions and predators. By being able to control the breeding conditions at all times, the fish farmer no longer has to worry about a cold wave killing the larvae or the low oxygen levels during the summer.
Finally, it is important to note the environmental advantages, such as the absence of leaks and controlled discharge of waste, since nearly all the water introduced into the system is reused, and less waste is produced compared to traditional systems.
For all these reasons, RAS farms will shape the future of aquaculture.