Next Tuna GmbH is planning, the first of its kind, production facility for Atlantic Bluefin Tuna (Thunnus thynnus) (ABT) at the shore of the Mediterranean Sea. (see as well https://www.nexttuna.com/).
Tuna in general and specially ABT is very sensitive to handling. In the early live stages, the small fish are nearly impossible to touch, and at later stages, the fish are simply too big to be handled in a meaningful way.
To address the logistic issue, Next Tuna, together with its Norwegian partner Seafarming system AS, developed the concept of a floating RAS. With the floating system, the fish can be collected at the hatchery and, when grown to the right size, transferred to a transport net-pen by joining the net-pen with the floating system. The flexibility of the floating systems solves the logistic challenges in tuna closed cycle aquaculture.
However, while developing the system adapted to the specific demands of ABT, next Tuan and its partner CM Aqua realized, that the floating facility might provide a solution to many challenges marine net-pen aquaculture is facing.
System description
The floating RAS, with a diameter of 30m and depth of 10m, is comparable in size with a net-pen however, the system is fully closed toward the surrounding environment through an insulated steel shell and covered by an industrial building (Fig. 1).
The floating RAS systems has two operational modes:
During production mode, the floating RAS receives all supplies from land or, if operated in open water, from a supply vessel, including, electricity, oxygen, new (sea) water and delivers all residuals back to land for final effluent water treatment (Fig. 2). For transport, the tanks are detached from harbour or supply vessel and tugged to destination.
The fish feed is supplied by net-pen feeders, which can be centrally loaded from the feed storage in the Next Tuna harbour and connected to each floating RAS. This gives a maximum of flexibility, with no additional infrastructure for feed supply needed.
The RAS effluent streams are further treated on land. In a sludge thickening station, the particulate matter from drum-filter backwash is separated from the liquid fraction and further processed in a biogas facility, while the liquid fraction, is treated together with the system effluent in a fixed bed biofilter, integrated with an IMTA approach (multitrophic integrated aquaculture) with macro algae.
The roof top of the floating RAS is used for solar panels, to supply the energy for the temperature control inside the RAS.
Climate resilient aquaculture
The floating RAS has the same size as a net-pen but is independent from the surrounding seawater temperature and quality. With only a minimum of new, pre-treated water supply the system is suitable for any marine fish production. It is thus resilient to adverse effects of climate change like heat waves, prolonged precipitation, algal blooms or water pollution. In addition, parasites and pathogens can be excluded with efficient inflow water treatment. Another advantage over open net-cages is that no uncontrolled effluents will be washed into the surrounding waters and escapees will not be an issue. This should help to tackle typical issues in permitting processes. Overall, the system will allow to take aquaculture closer to consumption, regardless availability of land or quality of water. In short, the floating RAS offers the advantages of a land-based RAS and adds the flexibility of a floating production platform.
The operation of the floating RAS is most suitable in harbour environments (Fig. 2) or sheltered areas with a max wave hight of 0.5m. However, design parameter can be adapted to allow operation more exposed places.
Discussion
Next Tuna wants to present this novel solution to marine aquaculture to the audience and discuss the chosen solutions and their implications with the experts present at the conference.