| Summary: | Increasing sea temperatures have been recorded globally during recent years presenting new challenges for aquaculture production. Fillet pigmentation loss in commercial harvest fish is concomitant with high water temperatures and reduced feed intake. Given that temperature is a major factor driving oxidative pressure in fish we hypothesised that salmon utilise carotenoids as antioxidants during prolonged thermal extremes. Therefore, we designed an in vivo model to test the potential of high dietary inclusion levels of the antioxidant vitamin E (α-tocopherol) to protect astaxanthin (Ax) and canthaxanthin (Cx), from depletion. Quadruplicate tanks of Atlantic salmon post-smolts (210 g) were satiation fed six diets and grown (to 560 g) at 15C for 11.5 weeks to initially load tissues with varying pigment and vitamin E levels. Fish were subsequently starved and water temperature increased to 19.5C for four weeks in a heat-challenge phase, simulating circumstances observed in situ. Six experimental diets contained three different inclusion levels of the carotenoids Ax and Cx: 1) 100 mg/kg Ax, 2) 100 mg/kg Cx and 3) 50 mg/kg Ax with 50 mg/kg Cx, each at two levels of vitamin E (500 and 1000 mg/kg). Fish (n=6/tank) were analysed pre and post heat-challenge for whole fillet (skinned, boned) concentrations of carotenoids and vitamin E. Fillets were digitized and converted to CIEL*a*b* colour space for analysis. Fillet carotenoid concentrations corresponded to dietary inclusion type and vitamin E concentrations were significantly increased by higher dietary inclusion. Fillet vitamin E concentrations increased significantly following heat-challenge whereas carotenoid concentrations were not significantly affected. Interestingly, image analysis revealed significantly reduced redness chromaticity (a*) for all treatments in anterior fillet regions, consistent with patterns in commercial fish at thermal extremes. Our results indicate that carotenoid depletion from fillets was not carotenoid specific and vitamin E provided limited protection against carotenoid depletion in vivo.
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