Introduction
Reducing aquaculture's reliance on marine resources such as fish oil and fish meal is a key objective for the industry, driven by cost and environmental footprint. However, substitute terrestrial (vegetable) oils lack crucial omega-3 long chain polyunsaturated fatty acids (n-3 LC-PUFA), especially eicosapentaenoic and docosahexaenoic acids (EPA and DHA, respectively) resulting in flesh with reduced n-3 content. This is undesirable for several reasons, linked to a negative impact on the health of the fish and flesh nutritional quality to humans. Plant biotechnological production platforms, in the form of genetically modified (GM) crops are now emerging as a viable alternative to either marine extraction or expensive algal fermentation (Napier and Betancor, 2023). Rothamsted research has developed several iterations of GM Camelina sativa accumulating high levels of EPA+DHA in its oil, and previously demonstrated the utility of these oils as an aquafeed ingredient for Atlantic salmon (Salmo salar; Betancor et al., 2015; Betancor et al., 2018). In the current trial a new iteration, in which the GM camelina fatty acid profile has been optimised to contain 20% EPA and DHA combined, was tested in Atlantic salmon for performance and health-promoting potential.
Materials and Methods
Figure 1. Proportions of rapeseed oil (RO), fish oil (FO) and GM camelina oil (CO) as a percentage of total oil in diets.
Three diets (Control, CO15 and CO30) were formulated with varying levels of fish oil (FO), omega-3 GM Camelina oil (CO) or rapeseed oil (RO) as a proportion of the total oil (Figure 1) and produced by Biomar. The diets were produced by hot extrusion with a blend of fish meal (FM), wheat, soy and crystalline amino acids, and oils were sprayed onto pellets by vacuum coating. Triplicated ambient temperature flowthrough 0.75 m2, 1.4 m diameter tanks of 55 post-smolt Atlantic salmon (starting weight 200 g) were fed these diets in excess for a total of 19 weeks until all fish had increased in weight at least 4-fold. Uneaten feed was collected daily to calculate feed intake and feed conversion rate (FCR) whilst biometric data recorded at the start and end of the trial was used to calculate growth and performance indices. At the end of the trial whole fish, Norwegian quality cut (NQC), and samples of liver and intestine were collected to evaluate composition (including fatty acid profile) and gene expression relating to nutrient uptake and health. In addition, whole fish were collected at the start of the trial to assess composition and calculate n-3 retention.
Results and Discussion
Weight gain and specific growth rate (SGR) were both higher in fish fed the CO15 diet than those fed the CO30 diet (P = 0.024 and P = 0.016 respectively). In contrast, FCR was lower in fish fed CO15 diet compared to CO30 (P = 0.048), indicating a more efficient uptake and assimilation of this diet. A higher energy content in flesh of fish fed the CO15 compared to those fed CO30 (P = 0.016) was complimented with corresponding differences in lipid levels (P = 0.016). Fatty acid levels (mirrored the diets fed to specific groups with higher levels of EPA in fish fed CO30 than those fed CO15 (P = 0.003) or Control (P = 0.009). However, whilst DHA levels were significantly lower in whole fish fed CO30 than other groups the difference in proportions was not as pronounced as in diets, likely due to low levels of biosynthesis as evidenced by the significantly higher retention, at 109%, compared to fish fed CO15 (93%; P = 0.037) and Control (77%; P = 0.044). Slightly lower growth performance of fish fed the CO30 diet may be related to levels of glucosinolates in the transgenic camelina oil (Betancor et al., 2021). However, better performance and higher absolute levels of total n-3 LCPUFA in fish fed CO15 compared to those fed Control (P = 0.002) demonstrate that this iteration of GM camelina oil functions well as part of a blend with fish oil and rapeseed oil in diets for Atlantic salmon.
Acknowledgment
This work was completed as part of the biotechnology and biological sciences research council (BBSRC) funded project OmegaBOOST "Camelina Omega-3 Oil for Optimal Heart and Gill Health" (BB/Z515322/1) in collaboration with colleagues at the Rothamsted Research, the University of Aberdeen and BioMar. The authors would like to thank the staff at MERL for their technical expertise during the running of the trial.
References
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