RAS is a recirculating aquaculture system. In the Soviet Union and still we use the term RAS. RAS – installation of closed water supply (water circulation).
At present, practically all over the world (including countries with a tropical climate) it is understood that successful and guaranteed managed and planned fish farming is possible only in the RAS.
In Ukraine, primarily due to economic reasons, the development of RAS has lagged behind global practice by 20-30 years. This is not about equipment, but about a competent approach to the design of RAS systems. Not a small role in this was played by the lack of competent, scientifically based information. Let’s try to understand what RAS is and try to deal with myths and mistakes.
In practice, RAS is a tank for growing fish and a water treatment system that includes mechanical and biological treatment, sterilization, temperature stabilization, oxygen saturation, looped into a single system. Usually topping up (and, accordingly, water discharge) per day is from 5 to 30% of the total volume of water in the system.
IMPORTANT!!! RAS should be designed not only for a specific type of farmed fish, but also for growing technology. What does it mean? Growing technology determines not only the quality of water in the system, the feeding regime, but also the final commercial sample of fish. For example, if you plan to grow sturgeon for caviar, you must understand what technology you will use to obtain caviar: by slaughtering females or by obtaining caviar in vivo. The same is true with the final sample of marketable fish. So if you are going to grow fish with a commercial sample of 500 gr and 1 kg, you should initially have a system designed differently. Unfortunately, there are NO universal systems!
What are the main requirements for designing a RAS?
-
-
- First of all, special attention should be paid to the water purification system. Here you need to clearly understand what type of mechanical cleaning filters (drum micromesh, belt or hydrocyclone) you will use.
- Next, you should decide on the type of biofilter used, which differ in the principle of operation and the type of bioload.
- The next point is how you will saturate the water with oxygen (air compressor, oxygen station or ozonator).
- Next – a method of water sterilization (ultraviolet lamps or ozonator).
- The next point is the volume and configuration of the pools for growing fish. An example – when growing sturgeon, the fundamental point is the bottom area, and when growing tilapia – the total volume of water, respectively, wide and shallow pools are needed for sturgeon, deep pools for tilapia.
-
In reality, there are still a lot of issues, for example, an auto-feeding system (separate feeders for each pool or a single pipeline with pneumatic feed supply), the same for automation systems and water quality control.