Terrestrial oils, which are used to replace fish oil in aquafeeds, are devoid in the health promoting omega-3 long chain polyunsaturated fatty acids (n-3 LC-PUFA) eicosapentanoic and docosahexaenoic acid (EPA and DHA, respectively) . Consequently, n-3 LC-PUFA levels have also decreased in the fish fillet. Concomitantly, a reduction in the fillet deposition of astaxanthin (AST), the pigment that donates the pinkish colour , was observed. Recent studies on a novel source of n-3 LC-PUFA using the oilseed crop Camelina sativa as a vehicle to produce EPA and DHA gave promising results to boost n-3 PUFA levels in fish fillet. This trial tested a new iteration of this transgenic oil containing EPA, DHA and also ketocarotenoids, predominantly AST, with the potential to increase fillet pigmentation in parallel to EPA and DHA levels.
Rainbow trout (Oncorhynchus mykiss; initial weight: 294 ±32 g) were divided into groups of 40 fish and allocated into quadruplicate tanks per treatment. Two experimental diets were tested, a control diet (CTL) containing 8% fish oil and 12% plant oils, according to commercial common practices, and a camelina oil diet (CAM) with only the transgenic oil at 20% inclusion. In addition, CTL, but not CAM was supplemented with synthetic AST (50 mg/kg ; Carophyll pink 10%, DSM) . Analysis of the experimental diets revealed that n-3 PUFA accounted for 21% of total fatty acids in CTL compared to 30% in CAM. Although AST levels were considerable higher in CTL compared to CAM (39±1 mg/kg vs 16±2 mg/kg) , total carotenoid levels were comparable between feeds (46±1 mg/kg in CTL vs 42±4 mg/kg in CAM) . The fish were fed the experimental diets over a period of 10 weeks. At the end of the feeding period, 10 fish were sampled for chemical and molecular analysis. In addition, 6 fish per tank were challenged in a swim tunnel prior to sampling . Performance parameters collected during the trial were complemented with measures of flesh quality including fatty acid and carotenoid levels as well as fillet colour profile.
Final body weight was not significantly different between treatments , although fish fed CAM were in tendency (p=0.06 , t-test) smaller compared to CTL (513±91 vs 537±106 g). Diet had no significant impact on exercise performance in the swim tunnel including tail beat counts or critical swimming speed. The fatty acid profile of the fillet reflected that of the diet with higher EPA and DHA levels in CAM compared to the CTL treatment. Fillet AST levels were significantly lower in CAM compared to CTL (Fig 1) . In accordance, colorimeter measures gave a significantly lower red value in CAM compared to CTL.
In conclusion, the transgenic Camelina oil effectively increased fillet EPA and DHA levels compared to a fish/terrestrial oil mix but resulted in lower fillet colour compared to synthetic AST supplementation.