Identifying alternatives with nutritional profiles similar to fish oil represents a major challenge for the Atlantic salmon farming industry. Such alternatives should be capable of overcoming issues like declining levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in farmed salmon fillets, a consequence of incorporating terrestrial plant oils into salmon diets. These plant oils are inherently low in omega-3 fatty acids, leading to a notable gap in the supply of omega-3 EPA and DHA. An ideal alternative, to overcome this nutritional deficiency, is the oil derived from Schizochytrium sp. In our feeding trial, we elucidated the effects of Schizochytrium sp.-derived oil (Veramaris® oil, VMO) on the growth and product quality of Atlantic salmon reared from their freshwater life phase to their harvest size in seawater.
A two-phase feeding trial was conducted at the research facility of LetSea AS in Dønna, Norway. During the 68-day freshwater (FW) phase, 4 experimental groups were offered one of four diets: 1) a control diet with 5.1% fish oil and 12% vegetable oil (0VMO); 2) a diet with 2.5% fish oil, 13.4% vegetable oil and 1.2% VMO (50VMO); 3) a fish oil-free diet, and containing 14.9% vegetable oil and 2.3% VMO (100VMO) and 4) the diet 100VMO, in which synthetic astaxanthin was replaced with algal astaxanthin (AA) (100VMO+AA). Fish with an average initial weight of 46 g were fed the experimental diets until they reached an average weight of 111 g. After this freshwater phase, the fish from all the groups were PIT tagged and randomly allocated to two groups of the seawater phase. These fish were held in two sea cages (400 fish/cage) and fed either the 0VMO diet or the 100VMO diet, adapted to the nutrient needs of the respective life stage. At the end of the 18 months experimental period, biometric data of all fish were recorded. Thereafter, 12 fish from each of the FW phase groups were sampled to assess fillet proximate and fatty acid composition. The effects of Schizochytrium sp.-derived oil incorporated salmon diets on product quality were also evaluated to assess it impact on the harvested fish.
Our results revealed that Schizochytrium sp. derived oil is as effective as fish oil, based on the data of feed intake, final weight, condition factor, specific growth rate, thermal growth coefficient and survival rates of the 0VMO and 100VMO groups. Fillet color analysis conducted with a Konica Minolta chroma meter provided information regarding the comparable levels of yellowness (b*) and lightness (L*) across the study groups. There were also indications that the diet containing Schizochytrium sp. oil, fed during the seawater phase, had a positive effect on the redness (a*) of the fillet of fish that had been fed the 100VMO+AA diet during the freshwater phase. Nevertheless, the SalmoFanTM measurements revealed that all the groups exhibited values within a narrow range of 26 to 26.5. Statistical analysis did not detect any significant differences in flesh texture or melanin spots. Our findings underscore the efficacy of a sustainable alternative to fish oil that is now considered a viable feed ingredient for salmon feeds.