The salmon aquaculture industry must be proactive at developing mitigation tools/strategies to offset the potential negat ive impacts of climate change. Therefore, this research examined if additional dietary cholesterol would: (1) enhance the upper thermal tolerance of female triploid Atlantic salmon (Salmo salar L. ), or their growth performance when exposed to elevated temperatures; (2) prevent/limit the fillet ‘bleaching’ (loss of astaxanthin) that has been observed in sea-caged fish exposed to high temperatures; or (3) affect fillet lipid and fatty acid content/profiles in the context of membrane fluidity, or basal and post-stress cortisol levels (the latter measured as cholesterol is the precursor of steroid hormones).
Salmon, initially acclimated to 12°C , were exposed to an incremental thermal challenge wherein temperature was raised by 0.2°C day-1 to mimic conditions that these fish experience when reared in sea-cages; with temperature held at 16 and 18°C for several weeks to prolong their exposure to elevated temperatures. From 16°C onwards, the fish were f ed either a control diet, or one of two n utritionally-equivalent experimental diets containing supplemental cholesterol (+1.30%, ED1 or + 1.76%, ED2 ). The additional dietary cholesterol did not improve the salmon’s incremental thermal maximum (ITMax) or growth , and may have negatively impacted survival ( at the highest inclusion level). In contrast, it reduced fillet ‘bleaching’ between 18°C and when the fish reached their upper temperature tolerance limit ( as measured using SalmoFan™ scores) as compared to fish fed the control diet.
Although further analyses are being conducted (e.g., fillet lipid class and fatty acid composition; plasma cortisol levels ), the current results suggest that supplementing salmon diets with cholesterol would have few/minimal benefits for the industry. That said, ≤ 5% of the female triploid Atlantic salmon used in this study died before temperature reached 22°C, and the mean temperature at which 50% mortality occurred was 23.2 + 0.1°C. Th ese latter data s uggest that it is possible to produce all female populations of rep roductively sterile salmon that can withstand summer temperatures that are likely to occur in Atlantic Canada.