FISH FARMING TECHNOLOGY
The highs and lows of RAS
by Daniel Jackson, Content Editor, International Aquafeed
“The earliest scientific
research on RAS was conducted
in Japan in the 1950’s”
Aquaculture is a rapidly growing industry; it will soon overtake wild fisheries as our dominant source of seafood. One of its main advantages is that it is more sustainable and environmentally friendly than traditional fish farming, which has high feed re-quirements, water use, and makes a significant impact on the local environment by re-leasing effluents. This is a problem that could be solved by the use of intensive recircu-lating aquaculture systems. Traditional saltwater aquaculture setups, in which fish are kept in tightly packed offshore pens, produce huge amounts of pollution. It is estimated to be equivalent to the raw sewage produced by a town of several thousand people, and it all flows directly into the ocean. In a recirculating aquaculture system (RAS) waste products are either used for other purposes (as a fertiliser for plant life, for example) or processed so that it can be recirculated. This saves money, resources and is better for the natural environment. In a standard setup water would first be filtered to remove any solid material, then passed through a biofilter to convert ammonia (which is excreted by fish) into nitrate. After leaving the vessel holding fish the water is first treated for solids before entering a bio-filter to convert ammonia, before degassing and oxygenation, often followed by heat-ing/cooling and sterilisation. Each of these processes can be completed by using a variety of different methods and equipment, but regardless all must take place to ensure a healthy environment that maximises fish growth and health.
History
The earliest scientific research on RAS was conducted in Japan in the 1950’s. These early trials focused on biofilter design for carp production and were driven by the need to use limited water resources more productively. At the same time European and American scientists attempted to adapt technology first developed for sewage treatment. Despite a strong belief by pioneers in the commercial viability of their work, most studies focused on science and the viability of the model in terms of chemistry. Furthermore,
34 | September 2019 - International Aquafeed