Abstract
Selection efforts focused on adaptation to plant-based diets, particularly the ability to synthesize polyunsaturated fatty acids (PUFA), are now emerging in aquaculture. Landlocked salmon (Grand Lake population; GL) may differ from the commercial Saint John River (SJR) strain in terms of PUFA metabolism. The objective of this study was to determine if GL salmon can contribute toward broodstock selection for enhanced PUFA synthesis. Two diets containing either fish oil (FO) or plant-based oil (FO-free) were fed to the SJR and GL strains (∼58 g/fish) for 16 weeks. Growth, liver, and muscle fatty acid (FA) content, and transcript expression of lipid metabolism and inflammation-related genes were evaluated. GL salmon fed the FO diet showed reduced growth compared to SJR salmon (fed either diet); however, GL salmon fed the FO-free diet, growth was not significantly different compared to any group. In liver, SJR salmon fed the FO-free diet had higher levels of n-6 PUFAs (21.9%) compared to GL fed the same diet (15.9%); while GL salmon fed the FO-free diet had higher levels of monounsaturated FAs (48.9%) compared with SJR salmon fed the same diet (35.7%). 20:5n-3 and 22:6n-3 were the same in GL and SJR salmon liver and muscle, respectively, fed the FO-free diet. In liver, GL salmon fed the FO-free diet had higher acac and acly compared to all treatments and had higher fasb compared to both strains fed the FO-diet. GL salmon fed the FO-free diet had higher cd36c and fabp3b in liver compared to GL salmon fed the FO diet and SJR salmon fed either diet. GL salmon fed the FO-free diet had higher lect2a and pgds in liver compared to SJR salmon fed the FO-free diet. In muscle, GL salmon fed the FO-free diet had higher fadsd5 and fadsd6b compared with both strains fed the FO diet. These results suggest there is a genetic basis behind the potential for GL salmon to utilize FO-free diets more efficiently than SJR salmon, with regards to FA metabolism.
Highlights
In North America, the Saint John River (SJR) strain of Atlantic salmon (Salmo salar L.) has been developed commercially since 1984 (Friars et al, 1995; Gjøen and Bentsen, 1997)
Dietary fish oil (FO) typically supplies the omega-3 (n-3) long chain polyunsaturated fatty acids (LC-PUFA), namely eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3), which are essential for vertebrates
FO derived from wild fisheries is rich in EPA and DHA, why it is the major source of these essential LCPUFA in commercial salmon feeds
Summary
In North America, the Saint John River (SJR) strain of Atlantic salmon (Salmo salar L.) has been developed commercially since 1984 (Friars et al, 1995; Gjøen and Bentsen, 1997). Terrestrial plants do not naturally produce n-3 LC-PUFA (Hixson et al, 2015) This is problematic for a carnivorous, anadromous species like Atlantic salmon, as these essential nutrients, that are normally provided by fish prey (in the wild) and FO (in aquafeeds), are lacking in plant-based ingredients (Tocher, 2015; Colombo, 2020). In aquaculture, this creates a mismatch between the nutrients in the diet ( the lack of n-3 LC-PUFA) and what is required by the fish for health and growth. Production of superior farmed fish that thrive on sustainable, plant-based diets, without the need to source n-3 LC-PUFA from the wild, is a logical research area in salmon aquaculture
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