The effect of dissolved carbon dioxide in Atlantic salmon (Salmo Salar) post-smolt performance, health and welfare reared in brackish water recirculating aquaculture systems

Control of dissolved CO2 is essential for design and management of recirculating aquaculture systems (RAS). On the one hand, CO2 removal from the water is costly and on the other hand, high CO2 concentrations are toxic for fish, affecting osmoregulation, stress status and growth performance. Although the maximum allowable dissolved CO2 in RAS is unknown. The effect of dissolved CO2 in Atlantic salmon (Salmo salar) post-smolt performance, health and welfare reared in brackish water RAS will be determined during a 12-week experimental period. Fish (initial body size ±100g, Salmobreed AS, Bolaks, Norway) will be exposed to six CO2 concentrations in a mono-factorial design, using three replicates per treatment. The experiment will be performed in small tank units (0.5 m3) to reduce the number of fish need and to increase the precision of observations. At the end of the 12-week experimental period, the effect of CO2 exposure in fish will be further assessed with three independent tests: 1) acute stress test; 2) physiological adaptation to CO2 free water during two weeks and; 3) seawater growth period during eight weeks. The response variables to measure include blood and tissues for ions and gene expression analysis, external welfare markers, growth and stress indicators.