Recirculation Aquaculture Systems (RAS) are dependent on a mature and robust biofilm within the bioreactor to efficiently convert harmful ammonium excreted by the fish . Furthermore, a biofilm matured for several years contributes strongly to a stable and diverse microbiota within the system, including fish tanks, which i s beneficial for the operational stability of the water treatment as well as for fish welfare.
The strategy of sustaining the biofilm in a RAS for several years is in theoretical conflict with the “all inn, all out” biosecurity principles due to a suspected potential of the biofilm to function as a reservoir for fish pathogens . The Norwegian regulations (NS-9416) define how a land-based aquaculture installation should be designed to avoid fish escap ing out of the facility and in to the wild . Hence, the main installations to avoid escapees are strategically placed sieves towards the facilities boundaries as well as in the fish tanks . Both set of sieves have light openings in relation to the minimum fish size defined by the production plan. I nternal escapees which have breached the primary barrier in the fish tanks, have shown to be residing in pipes, drum-filters, bioreactors, CO2-degassers and oxygen-cones within a RAS department .
Pure Salmon Technology (PSTech) has the past year high-lighted the potential of internal escapees in RAS to breach the biosecurity principle of “all inn, all out”. In a field study of two In fectious pancreatic necrosis virus (IPNV) infected RAS-departments in a n Atlantic salmon Salmo salar Norwegian hatchery, we demonstrated that internal escapees were sub-clinically infected by IPNV . These individuals would serve as a reservoir for the virus and thus pose a risk for the new batch of fish introduced into the department .
Based on the presented case study and similar experiences by other smolt producers in Norway, we will document why internal escapees within RAS must be removed before any biosecurity measures are taken towards the biofilm in the bioreactor. “Humane” euthanasia solutions (using approved sedative at high dose) procedures will be presented to help eliminate individuals acting as potential pathogenic hosts in the system without compromising the biofilter efficiency and performance.