UBC Theses and Dissertations
The effect of salinity and photoperiod on thermal tolerance and growth of Atlantic and coho salmon reared from smolt to adult in recirculating aquaculture systems. Hines, Chandler William
Land-based, closed containment salmon aquaculture involves rearing salmon from smolt to adult in recirculating aquaculture systems (RAS). Unlike in open-net pen aquaculture, rearing conditions can be specified in RAS in order to decrease physiological stress. The environmental conditions that yield optimal growth and physiological stress tolerance in salmon are, however, unknown. To address this knowledge gap, we reared Atlantic (Salmo salar) and coho (Oncorhynchus kisutch) salmon in 7 separate RAS for 400 days post-smoltification under 2 photoperiods (12 or 24 hours of light) and 4 salinities (2.5, 5, 10 or 30 ppt) and assessed the effects of these conditions on growth and thermal tolerance. We found that salinity and photoperiod had significant effects on growth of Atlantic and coho salmon, but optimal conditions were not determined. Secondly, we found Atlantic salmon generally grew best under 24 hours of light until day 400 when the trend was lost and that coho salmon grew best under 12 hours of light in the freshwater (2.5 ppt) treatment. Finally, we found higher levels of maturation in Atlantic salmon reared under 24 hours of light, whereas the 12:12 photoperiod triggered greater levels of early maturation in coho. In order to evaluate the effects of photoperiod and salinity on the physiological stress tolerance we used critical thermal maxima or CTmax tests as a performance proxy. We found that over the first 120 days post-smoltification, rearing coho under a 24 hour photoperiod resulted in a ~2°C lower CTmax than in coho reared under a 12:12 photoperiod. This photoperiod effect did not persist at 200 and 400 days, which was coincident with an overall decrease in CTmax in coho salmon relative to 120 days. Finally, Atlantic salmon had a higher CTmax (~28°C) compared to coho (~26°C) at 400 days post-smoltification. Overall, these findings are important for the future implications of RAS and for the aquaculture industry to help identify physiologically sensitive time stages.
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