The expected outcomes will improve risk assessment and biosecurity protocols in these systems by identifying the dynamics of infection. This will further support the development of RAS as a viable technology for salmon production on land. In addition, the results are also expected to provide new insights to the feed companies on the importance of the physical qualities of the pellets used in RAS. On a more fundamental basis, new knowledge about the immune response to IPNV in complex environments such as RAS will advance our understanding in fish virology.

Fish that have been bath-challenged with IPNV will develop the pathologies related to the disease, and less robust fish may expire. Fish that will be exposed to the challenged fish may develop pathologies, and those less robust may also expire. We do not expect high mortality rates since the infection trial will not last longer than 6 weeks, which is relatively shorter compared with many virus infection trials.

All animals for sampling will be euthanised since tissue samples will be collected for molecular and histological analyses. These analyses can only be carried out in euthanised specimens. The remaining fish after the trial will be euthanised. This is to avoid the worsening of the pathologies.

The number of fish requested is the minimum number of samples to give reliable scientific results and support optimum system performance. The experimental units to be used in the trial have been designed to mimic a small-scale RAS unit but are still able to incorporate parameters relevant during commercial production.

Viral infection studies often last for a minimum of 10 weeks. The infection trial in this study will not last longer than 6 weeks, and severe pathologies will not be allowed to progress. With the proposed approaches, mortality may occur in less robust fish, but we do not expect high cumulative mortality (>30%). The physico-chemical quality parameters that support the fish biological requirements such as oxygen, water flow, pH, NH4, CO2, to name a few will be maintained at optimum level to rear Atlantic salmon post-smolt (see attachment 1). Routine monitoring of these parameters will ensure that they are kept at optimal levels. Due to differences in feed quality, we expect higher turbidity in the group to be fed with a diet with low binder. Therefore, we set a maximum turbidity threshold. If the level reaches a level beyond this threshold, we will increase either the water flow or the daily water exchange until the desired turbidity is reached. Moribund fish (see definition in the endpoint criteria) will be removed from the tanks and euthanised.

The trial is designed to provide the necessary information for improving biosecurity measures for RAS-based farming during the post-smolt stage (specifically brackish water) of salmon production. Therefore, only salmon adapted to brackish water is the appropriate model for this trial.

De mest belastede laks forventes å utsettes for betydelig belastning.