Synergistic effects of dietary iron and omega‐3 fatty acid levels on survival of farmed Atlantic salmon, Salmo salar L., during natural outbreaks of furunculosis and cold water vibriosis

Abstract

The present study demonstrates that farmed Atlantic salmon, Salmo salar, health is positively and significantly affected by synergistic effects between very long-chain polyunsaturated fatty acids of the n-3 family eicosapentaenoic acid/docosahexaenoic acid (EPA/DHA) and iron, where positive effects of high dietary levels of EPA/DHA are enhanced when combined with low levels of iron. Based on cumulative mortalities in the different experimental groups, relative percentage of survival (RPS) for the high EPA/DHA-low iron group was 70% during an outbreak of furunculosis and 96% during an outbreak of cold water vibriosis compared with the controls. A non-additive effect between EPA/DHA and iron was confirmed by statistical analyses that revealed a significant effect of EPA/DHA alone and an interaction of iron with EPA/DHA. Liver cell cultures treated with EPA/DHA revealed that the synergistic effect could be related to an EPA/DHA dependent regulation of mRNA for proteins important for transport (transferrin) and storage (ferritin) of iron in the salmon. In keeping with this finding, the transcriptional down-regulation of iron metabolism in vitro was reflected in decreased in vivo iron stores with increasing levels of dietary EPA/DHA. Hence, to avoid overloading of the iron transport/storage-systems resulting in increased susceptibility to bacterial infections, high levels of dietary EPA/DHA should be accompanied by low levels of dietary iron.

A Piece of the Puzzle—Possible Mechanisms for Why Low Dietary EPA and DHA Cause Hepatic Lipid Accumulation in Atlantic Salmon (Salmo salar)

“…We found indications of a higher inflammatory status in fish fed diets 1.0 and 1.6 than in fish fed diet 3.5. Similarly, other studies have shown that a reduced dietary inclusion of EPA + DHA can result in an increased inflammatory response [69][70][71][72][73]. EPA + DHA at the highest level (diet 3.5) greatly ameliorated all metabolic health issues investigated in the present trial; these fish did not have hepatic lipid accumulation, had a normally functioning lipid metabolism, reduced inflammatory metabolite markers and they achieved significantly higher final weights.…”

Does the capacity for energy utilization affect the survival of post‐smolt Atlantic salmon, Salmo salar L., during natural outbreaks of infectious pancreatic necrosis?

“…We have previously documented that Atlantic salmon survival during a natural outbreak of furunculosis, caused by Aeromonas salmonicida , and cold‐water vibrosis, caused by Vibrio salmonicida , was strongly affected by dietary treatments (Rørvik, Dehli, Thomassen, Ruyter, Steien & Salte 2003). Positive effects of high dietary levels of long‐chain polyunsaturated fatty acids of the n‐3 family (EPA/DHA) were enhanced when combined with low levels of iron.…”

Effects of eicosapentaneoic acid on innate immune responses in an Atlantic salmon kidney cell line in vitro

“…The downregulation of this complex in the EPA/poly I:C treated cells combined with upregulation of the transferrin receptor (hence increased iron uptake) may therefore explain the enrichment of ferroptosis related transcripts observed here. Interestingly, synergistic effects between low dietary iron and high omega-3 fatty acids related to iron storage capacity were observed during natural outbreaks of bacterial disease in Atlantic salmon [ 97 ].…”