Eldar Åsgard Bendiksen

Digestibility, growth and nutrient utilisation of Atlantic salmon parr (Salmo salar L.) in relation to temperature, feed fat content and oil source

Digestibility, growth and nutrient utilisation of Atlantic salmon parr (Salmo salar L.) in relation to temperature, feed fat content and oil source

Effects of dietary fatty acid profile and fat content on smolting and seawater performance in Atlantic salmon (Salmo salar L.)

Abstract An experiment was conducted to study the effects of dietary fat level and fatty acid composition on seawater acclimation and growth in Atlantic salmon. Marine fish oil or a blend of rapeseed and linseed oils were added to extruded pellets to produce four feeds differing in fat content (LF: 21% and HF: 34%) and fatty acid composition. The feeds were designated LFFO, LFVO, HFFO and HFVO according to fat level (LF—low fat; HF—high fat) and oil source (FO—fish oil; VO—vegetable oil). Each feed was fed to salmon parr (∼19 g) held at 2 °C on a 12L:12D regime for 6 months. Parr–smolt transformation was then induced by increasing the photoperiod from 12L:12D to 24L:0D, and water temperature to 8 °C. Fish fed the four feeds grew at similar rates both during the parr stage (SGR; 0.40±0.01) and during the smoltification period (SGR; 0.64±0.01). Fish fed the high-fat feeds had a higher percentage body fat than fish fed low-fat feeds, and fatty acid profiles resembled those of the feed. Parr–smolt transformation was accomplished within 3 weeks after change in photoperiod in all groups, as assessed by gill Na+,K+-ATPase activity, muscle water and plasma chloride following 24-h seawater tests. During the 42-days seawater period the fish were fed either LFFO or HFFO feed. Groups of 50–60 fish were subjected to one of eight feed treatments: no dietary shift, shift in feed oil type, shift in feed fat (energy) content or shift both in feed oil type and feed fat content at the time of seawater transfer. Fish in all groups lost weight during the first 3 weeks in seawater, but fish fed the LFVO feed (i.e. low-fat vegetable oil) during freshwater rearing gained weight during the total 6-week seawater period. Significantly better growth and a significantly higher proportion of fish with positive growth rates than in other treatments was, however, only seen in the group in which a shift in both lipid source (from VO to FO) and feed fat content (from LF to HF) had been applied. Whether this was an effect of increased supply of n−3 HUFAs or dietary energy, or a combination of both factors, is not clear. There were no significant differences in plasma chloride or plasma osmolality between groups during seawater residence or in gill Na+,K+-ATPase activity at the end of the seawater period.

Effects of decontaminated fish oil or a fish and vegetable oil blend on persistent organic pollutant and fatty acid compositions in diet and flesh of Atlantic salmon ( Salmo salar).

The health benefits of seafood are well documented and based on the unique supply of n-3 highly unsaturated fatty acids (HUFA). Aquaculture now contributes about 50 % of food-grade seafood globally and Atlantic salmon (Salmo salar) is a rich source of n-3 HUFA. However, salmon and other oily fish can accumulate lipophilic persistent organic pollutants (POP), including dioxins (PCDD/F), polychlorinated biphenyls (PCB) and polybrominated diphenyl ethers (PBDE), derived largely from feed. In the present study, triplicate groups of salmon, of initial weight 0.78 kg, were fed one of three experimental diets for 11 weeks. The diets were coated with either a northern fish oil (FO) with a high POP content (cNFO), the same oil that had been decontaminated (deNFO) or a blend of southern fish oil, rapeseed and soyabean oils (SFO/RO/SO). Dietary PCDD/F+dioxin-like PCB (DL-PCB) concentrations were 17.36, 0.45 and 0.53 ng toxic equivalents (TEQ)/kg, respectively. After 11 weeks, the flesh concentrations in fish fed the cNFO, deNFO and SFO/RO/SO diets were 6.42, 0.34 and 0.41 ng TEQ/kg, respectively. There were no differences in flesh EPA and DHA between fish fed the cNFO or deNFO diets although EPA and DHA were reduced by 50 and 30 %, respectively, in fish fed the SFO/RO/SO diet. Thus, decontaminated FO can be used to produce salmon high in n-3 HUFA and low in POP. Salmon produced using deNFO would be of high nutritional value and very low in POP and would utilise valuable fish oils that would otherwise be destroyed due to their high pollutant concentrations.