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As fish oil is an increasingly limited input-factor, content of the n-3 fatty acids eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) is being gradually reduced in feeds for farmed salmon, and consequences for fish health and fillet quality need to be addressed. In the present study, Atlantic salmon (Salmo salar L.) were fed two levels of EPA and DHA through the seawater rearing period from six weeks after smolt transfer (~ 150 g) until harvest (~ 5000 g). The trial was conducted under commercial production conditions, with triplicate net pens used for each diet group. The control (standard) diet contained 8% EPA + DHA of total fatty acids (FAs, 26 g kg− 1 feed), while the low n-3 diet contained 6% EPA + DHA of FAs until 1200 g body weight and 4.5% in following feeds, averaging out to 5% of FAs (16 g kg− 1 feed) during the entire production cycle. Growth performance and measured health parameters including cataract, liver lipid accumulation and vaccine side-effects did not differ significantly between the two diet groups. Through the production period, the fish faced stressful and challenging conditions such as five treatments against sea lice (one oral and four bath treatments), as well as an outbreak of pancreas disease and considerable mortality from gill infections. Despite this, mortality did not differ significantly between the diet groups, indicating that fish fed low dietary n-3 FAs were equally robust as fish fed the standard diet. Quality classification at slaughter did not reveal any diet effects, and neither did sensory evaluation of the fish fillets. As expected, the fillet FA profile differed, with 5.4% EPA + DHA of total FA (0.9 g 100 g− 1) in the fillet of fish fed the low n-3 diet and 7.5% (1.3 g 100 g− 1) in fish fed the standard diet. The fish fed low EPA + DHA showed a higher frequency of fillet melanin spots, 28.2%, compared to 21.5% in the salmon fed the standard diet, possibly related to dietary FA composition affecting inflammatory processes. Statement of relevance Supply of fish oil is limiting growth of the salmon industry

One hundred farmed Atlantic salmon, Salmo salar L., were examined for the presence of nematodes by digestion of tissue in HCl-pepsin solution. All fish were sampled from one cage in a fish farm on the Norwegian south-west coast. Fifty harvest quality salmon, that is, salmon for human consumption (mean 5.4 kg, variation 3.0-7.6 kg), were sampled at the processing line while 50 salmon runts (mean 1.1 kg, variation 0.4-1.8 kg), discarded due to poor performance, were sampled from the discard bin after the grading station. Runts are individual fish with clear signs of poor performance over time and abnormal appearance and are thus not processed for human consumption. No nematodes were found in the musculature or viscera of the 50 harvest quality salmon. In total, 75 nematodes were found in 10 (20%) of the runts; 53 nematodes in the viscera and 22 in the musculature. Nematodes in the musculature were identified as Anisakis simplex (Rudolphi, 1809 det. Krabbe, 1878), while nematodes in the viscera were identified as A. simplex and Hysterothylacium aduncum (Rudolphi, 1802).

In a 17-week experiment with Atlantic salmon (2.3–5.2 kg) in sea cages, a diet containing European animal by-products and salmon oil (ABP) was compared with a control diet based on fish and plant ingredients, with respect to performance and product quality. Fish fed with the ABP diet had similar growth rates, but slightly improved feed conversion ratio (feed: gain; 1.08 versus 1.14) compared with the control. No differences were seen in fish length, live weight or condition factor. Final body composition was similar and retention of nitrogen and energy did not differ between diets. Higher DPA (C22:5 n-3) content in the ABP diet apparently inhibited conversion of EPA (C20:5 n-3) to DPA, resulting in higher EPA retention in muscle and whole body. Muscle and whole body DHA (C22:6 n-3) level and n-3 : n-6 ratio were higher in the ABP group, corresponding with dietary levels. There were no differences in slaughter yield, quality classification, gaping score or fillet texture between diets. The feed with ABP contained less astaxanthin, possibly because of degradation catalyzed by iron in blood meal, and this resulted in lower muscle colour score and astaxanthin concentration (4.6 versus 6.4 mg kg−1). A sensory test did not reveal any differences in odour, flavour, or texture.

One hundred farmed Atlantic salmon, Salmo salar L., were examined for the presence of nematodes by digestion of tissue in HCl-pepsin solution. All fish were sampled from one cage in a fish farm on the Norwegian south-west coast. Fifty harvest quality salmon, that is, salmon for human consumption (mean 5.4 kg, variation 3.0-7.6 kg), were sampled at the processing line while 50 salmon runts (mean 1.1 kg, variation 0.4-1.8 kg), discarded due to poor performance, were sampled from the discard bin after the grading station. Runts are individual fish with clear signs of poor performance over time and abnormal appearance and are thus not processed for human consumption. No nematodes were found in the musculature or viscera of the 50 harvest quality salmon. In total, 75 nematodes were found in 10 (20%) of the runts; 53 nematodes in the viscera and 22 in the musculature. Nematodes in the musculature were identified as Anisakis simplex (Rudolphi, 1809 det. Krabbe, 1878), while nematodes in the viscera were identified as A. simplex and Hysterothylacium aduncum (Rudolphi, 1802).