By Cecilia C. Vargas*
Recirculating systems vary in the degree of recirculation from RAS low, intensive and super intensive levels, having degrees of recirculation at system (vol. recycled one time per hour) of 95.9, 98.6 and 99.6 % respectively. Building and operating RAS systems are costly affairs. Therefore, selecting the right fish species to produce by RAS is of great importance. Species with high market prices and demand as well as any fish reared successfully in traditional aquaculture should be good candidates.
In Norway, RAS is mainly used for smolt production of Atlantic salmon and with great success. The number of RAS facilities are increasing and new RAS facilities are built to produce post-smolts with sizes up to 1kg. However, producing marine fish species in RAS in Norway has not given satisfactory results. For instance, there have been a few attempts at producing Atlantic halibut and Atlantic cod without success. This leads to questioning what we are doing wrong or what we need to consider when planning to operate RAS for marine fish species?
Dr. Kari Attramadal, researcher at Sintef Fisheries and Aquaculture and expert in RAS for marine fish species, points out that knowing the differences between running RAS in freshwater and seawater are crucial. Seawater has a higher buffering capacity and alkalinity than freshwater. However, ozonation (above a certain dose) forms harmful residual oxidants. The difficulty to ventilate the CO2 requires that aerators must be dimensioned slightly larger and there are secondary bacterial species responsible for nitrification compared to freshwater. The biofilter may take a little longer to start up and may be slightly less effective (biofilter should be dimensioned slightly larger) but protein skimmers on the other side, work much better and are effective for removing small particles, bacteria and organic materials in sea water.
Other bacteria and parasites are more problematic than in freshwater. However, problems associated with fungus are much less than in freshwater, and nitrite is less toxic. Dr. Attramadal remarks that focus should be on very clean water and systems adapted specifically to marine fish species rather than using old systems that were designed for salmon or freshwater species. For many marine species very clean water with few particles and little organic material is a key consideration. This is true to a much greater extent than with salmon, which means that particle removal and purification must be better in marine RAS. RAS require high knowledge levels and therefore the importance here in Norway, and elsewhere, is to have personnel who can design and operate these systems.
Lately, the boom in facilities along the Norwegian coast to produce lumpfish has led to an increasing interest in using RAS to produce this species. Atlantic Lumpus, the first company using RAS for lumpfish production, has just started its operations. Dan Kristian Larssen (Manager Director), explains that the facility was planned with a strong focus on flexibility, both technically and in layout. All essential parameters like salinity, oxygen, temperature, carbon dioxide and pH can be adjusted with simple actions, in each department. Overall, the facility has 6 physically separated production areas, each with a water treatment configuration that is independent of the others. All components are also mounted above the floor (nothing set in concrete), which allows changing the plan without major ‘surgery.’ Based on this, the facility can theoretically produce cod, wolf fish, lumpfish, halibut, or even salmon. The RAS have recycling rates of 94-98 % due to energy-efficient construction considerations. The facility has not been operating long enough to experience specific challenges in the use of RAS. However, Larssen is aware of the challenges that can appear when running these advanced systems, where multiple components need to work together to function properly. Until now everything is going very well and he is very satisfied with the support from the RAS supplier, Billund Aquaculture Service.
The best of luck to Atlantic Lumpus and here’s hoping that other companies producing marine fish species follow its path.
Cecilia C. Vargas is currently R & D Manager at Helgeland Havbruksstasjon in Sandnessjøen, Norway. She has many years of experience in production of aquatic species including rainbow trout, Atlantic salmon, cod, various Japanese fishes, and live feed production. Her PhD studies focused on differences between diploid and triploid Atlantic cod in digestive and muscle systems. e mail: firstname.lastname@example.org