Microalgae and organic minerals enhance lipid retention efficiency and fillet quality in Atlantic salmon (Salmo salar L.)

Abstract Pure spray dried DHA rich microalgae biomass ( Schizochytrium sp. ) was used to replace fish oil as a source of long chain n-3 polyunsaturated fatty acids (n-3 LC-PUFA) in medium (150 g kg − 1 ; MF) and low fish (100 g kg − 1 ; LF) meal diets for Atlantic salmon post smolt supplemented with either inorganic or organic minerals (OM: Zn, Cu, Mn, Fe and Se). The diets were balanced for total saturated fatty acids (SFA), sum DHA + EPA and n-3/n-6 ratio and had similar protein and energy digestibility and high pellet technical quality. Lipid digestibility was above 90% in all diets, nevertheless 2.3% lower in the diet containing 50 g kg − 1 microalgae, compared to the control, mainly due to the lower digestibility of SFA in the microalgae rich diets. The experimental fish grew from 0.4 kg to 1.1 kg with no significant differences in growth rate (TGC 3.7–3.8) or feed conversion ratio (FCR 0.7) among the dietary treatments. The retention efficiency of EPA + DHA in salmon body was significantly improved in the fish fed diets containing increasing levels of microalgae, and thus lower EPA/DHA ratios. Moreover, liver lipid levels were decreased and dress-out percentage increased by increasing microalgae dietary supplementation level. The fillet levels of SFA and DHA + EPA were similar for all treatments. Improved fillet quality in terms of lower gaping scores was observed with increasing dietary inclusion level of Schizochytrium sp. and even more pronounced for salmon fed organic minerals. No significant effects on fish blood plasma chemistry and whole body mineral content were observed. Statement of relevance Aquaculture is in urgent need of adequate volumes of new LCn-3PUFA sources, alternative to fish oil. The current work documents the feasibility of using practically relevant levels of heterotrophic microalgae as LCn-3PUFA source in the diet of Atlantic salmon in terms of extruded feed production feasibility, general fish performance, fish fillet product quality (nutritional and technical), nutrient retention efficiency and blood chemistry.