Performance of Atlantic salmon post-smolts reared in RAS with nanofiltered sulfate-reduced brackish water

Sammendrag

Hydrogen sulfide (H2S) accumulation in brackish water Recirculating Aquaculture Systems (RAS) poses a significant risk to the commercial production of Atlantic salmon (Salmo salar) due to potential mortality events. Nanofiltration to remove sulfate has been proposed to mitigate H2S formation risk, but the technology has an impact on water ionic composition and its consequences in fish physiology remain unexplored. This study examined the performance of Atlantic salmon post-smolts (72.6 ± 8.8 g) reared in nanofiltered sulfate-reduced brackish water (S- BW) at 15 PSU over four months, monitoring growth, gene expression of growth related genes, blood biochemistry, stress responses and bone health. Fish reared in normal brackish water (S+ BW) served as controls. Results showed no significant difference in overall fish growth (weight: 378 ± 75.0 vs 386 ± 70.6 g; length: 30.6 ± 2.1 vs 30.8 ± 1.8 cm; condition factor: 1.30 ± 0.11 vs 1.31 ± 0.10 g cm−3) between treatments after four months. Both divalent and monovalent plasma ion concentrations were consistently lower in the blood of the S- BW reared fish. Reduced stress response, indicated by lower water cortisol levels after transfer, suggests S- BW may provide a smoother transition environment. Vertebrae analyses indicated a potential risk of decreased stiffness and increased hyperradiodense malformation frequency in S- BW reared fish. Both stiffness reduction and hyperradiodense malformation may be reversible under appropriate environmental conditions. Therefore, further study beyond the observed four-month period is necessary to apply this technology for longer periods.