Effects of salinity and photoperiod on growth, aerobic scope, and hypoxia tolerance of Atlantic and coho salmon in recirculating aquaculture systems

Recirculating aquaculture systems (RAS) are an emerging technique in aquaculture to rear salmon in land-based facilities, but the systems are also associated with high costs, so rearing fish under optimal conditions for maximum growth is required for profitability. However, few systematic studies have been conducted to determine optimal conditions for growth of salmon from smolt through to market size in RAS and the related effects on physiological performance. To address this knowledge gap, the first part of my thesis investigated the effect of salinity on growth, metabolism and hypoxia tolerance of Atlantic and coho salmon. Smolts were reared at salinities of 0, 5, 10, 20 and 30 ppt under 24 h of light in RAS for up to 460 days. Between Days 200 and 400, respirometry was conducted to measure routine, maximum metabolic rate and aerobic scope, while time to loss of equilibrium at 10% air saturation was measured to determine hypoxia tolerance. The initial effect of salinity on growth was found in Atlantic and coho salmon at Day 295 and 59, respectively, after which growth was generally enhanced at intermediate salinities of 5 and 10 ppt. No clear relationship was found between salinity and metabolic measurements in either species. Hypoxia tolerance of Atlantic salmon was enhanced at 5 and 10 ppt, but salinity had no effect on hypoxia tolerance of coho salmon. The second part of this thesis aimed to (1) determine metabolism and hypoxia tolerance of coho salmon during their early growth stages where the effect of salinity on growth was the most profound and (2) explore the interactive effect of photoperiod. A new cohort of coho salmon smolts were reared in RAS at 2.5, 5, 10 and 30 ppt under 12:12 and 24:0 (light:dark) photoperiods, while respirometry and hypoxia trials (15% air saturation) were conducted at Day 60 and 120. No effect of salinity and photoperiod was found on metabolic measurements and hypoxia tolerance in the younger coho salmon during these periods. Overall, my data suggest that there is some potential to enhance growth of salmon by manipulating environmental conditions in RAS without compromising other physiological performance.Science, Faculty ofZoology, Department ofGraduat