Influence of Supplemental Dietary Cholesterol on Growth Performance, Indices of Stress, Fillet Pigmentation, and Upper Thermal Tolerance of Female Triploid Atlantic Salmon (Salmo salar)

The salmon aquaculture industry must be proactive at developing mitigation tools/strategies to offset the potential negative impacts of climate change. Therefore, this study examined if additional dietary cholesterol could enhance salmon production at elevated temperatures. We hypothesized that supplemental cholesterol could aid in maintaining cell rigidity, reducing stress and the need to mobilize astaxanthin muscle stores, and improving salmon growth and survival at high rearing temperatures. Accordingly, postsmolt female triploid salmon were exposed to an incremental temperature challenge (+0.2 degrees C day(-1)) to mimic conditions that they experience in sea cages in the summer, with temperature held at both 16 and 18 degrees C for several weeks [i.e., 3 weeks at 16 degrees C, followed by an increase at 0.2 degrees C day(-1) to 18 degrees C (10 days), then 5 weeks at 18 degrees C] to prolong their exposure to elevated temperatures. From 16 degrees C onwards, the fish were fed either a control diet, or one of two nutritionally equivalent experimental diets containing supplemental cholesterol [+1.30%, experimental diet (#)1 (ED1); or +1.76%, experimental diet (#)2 (ED2)]. Adding cholesterol to the diet did not affect the salmon's incremental thermal maximum (ITMax), growth, plasma cortisol, or liver stress-related transcript expression. However, ED2 appeared to have a small negative impact on survival, and both ED1 and ED2 reduced fillet bleaching above 18 degrees C as measured using SalmoFan (TM) scores. Although the current results suggest that supplementing salmon diets with cholesterol would have few/minimal benefits for the industry, <= 5% of the female triploid Atlantic salmon used in this study irrespective of diet died before temperature reached 22 degrees C. These latter data suggest that it is possible to produce all female populations of reproductively sterile salmon that can withstand summer temperatures in Atlantic Canada.

Automated summary

This study examined the effects of adding dietary cholesterol on salmon production at elevated temperatures. The results showed that adding cholesterol did not significantly affect thermal maximum, growth, or stress response in the fish. However, it had a small negative impact on survival and fillet bleaching. Nevertheless, the study also found that less than 5% of the female triploid Atlantic salmon used in the study died before temperatures reached 22°C, suggesting the possibility of producing all female populations of reproductively sterile salmon that can tolerate summer temperatures.