Low levels of very-long-chainn-3 PUFA in Atlantic salmon (Salmo salar) diet reduce fish robustness under challenging conditions in sea cages

Abstract

The present study aimed to determine the minimum requirements of the essential n-3 fatty acids EPA and DHA in Atlantic salmon (Salmo salar) that can secure their health under challenging conditions in sea cages. Individually tagged Atlantic salmon were fed 2, 10 and 17 g/kg of EPA + DHA from 400 g until slaughter size (about 3·5 kg). The experimental fish reared in sea cages were subjected to the challenging conditions typically experienced under commercial production. Salmon receiving the lowest EPA + DHA levels showed lower growth rates in the earlier life stages, but no significant difference in final weights at slaughter. The fatty acid composition of various tissues and organs had remarkably changed. The decreased EPA + DHA in the different tissue membrane phospholipids were typically replaced by pro-inflammatory n-6 fatty acids, most markedly in the skin. The EPA + DHA levels were maintained at a higher level in the liver and erythrocytes than in the muscle, intestine and skin. After delousing at high water temperatures, the mortality rates were 63, 52 and 16 % in the salmon fed 2, 10 and 17 g/kg EPA + DHA. Low EPA + DHA levels also increased the liver, intestinal and visceral fat amount, reduced intervertebral space and caused mid-intestinal hyper-vacuolisation. Thus, 10 g/kg EPA + DHA in the Atlantic salmon diet, a level previously regarded as sufficient, was found to be too low to maintain fish health under demanding environmental conditions in sea cages.

Are we what we eat? Changes to the feed fatty acid composition of farmed salmon and its effects through the food chain

“…Despite this in vivo production, preformed long-chain n-3 PUFA are required for optimal growth, fish health and tissue integrity during long-term feeding in salmon Sissener et al, 2016b;Bou et al, 2017a). Although survival was high (>99%) when low EPA+DHA (≤1% of the feed) were used in land-based tanks with controlled and optimal conditions , high levels of fish mortality occurred when the same levels were fed to fish in open net pens with fluctuating environmental conditions and stressful handling of the fish (Bou et al, 2017b). Such a reduction in fish robustness and survival means that it is highly unlikely that these low levels would be implemented in commercial culture; hence it is likely that feed with a minimum level of >1% EPA+DHA will be maintained.…”

n-3 Canola oil effectively replaces fish oil as a new safe dietary source of DHA in feed for juvenile Atlantic salmon

“…An additional benefit of DHA-CA compared with conventional canola oil is the lower levels of n-6 FA, which results in lower body levels of n-6 FA when included in the diet. The n-6 FA are linked to pro-inflammatory pathways and generally tend to bio-accumulate with the use of terrestrial plant oils to replace FO (37) . The muscle tissue showed similar trends to the FA profiles of those of the whole body, except for lower relative percentages of MUFA and higher percentages of n-3 PUFA.…”

Effects of dietary alpha-linolenic acids on growth performance, lipid metabolism and antioxidant responses of juvenile Russian sturgeonAcipenser gueldenstaedtii

“…As LNA is the precursor for EPA and DHA synthesis, the diets rich in LNA can increase the contents of EPA and DHA in grass carp and Nile tilapia (Lei, Tian, Ji, Chen, & Du, ). Tissue DHA and EPA play a key role in maintaining fish health through their participation in cell synthesis, neural tissue function and development, ontogenesis and endocrine and immune system function (Bou et al., ; Glencross, ; Tocher, Dick, Bron, Shinn, & Tocher, ).…”