Effects of functional feeds on the lipid composition, transcriptomic responses and pathology in heart of Atlantic salmon (Salmo salar L.) before and after experimental challenge with Piscine Myocarditis Virus (PMCV)

Abstract

BackgroundCardiomyopathy syndrome (CMS) is a severe cardiac disease of Atlantic salmon (Salmo salar) recently associated with a double-stranded RNA virus, Piscine Myocarditis Virus (PMCV). The disease has been diagnosed in 75-85 farms in Norway each year over the last decade resulting in annual economic losses estimated at up to €9 million. Recently, we demonstrated that functional feeds led to a milder inflammatory response and reduced severity of heart lesions in salmon experimentally infected with Atlantic salmon reovirus, the causal agent of heart and skeletal muscle inflammation (HSMI). In the present study we employed a similar strategy to investigate the effects of functional feeds, with reduced lipid content and increased eicosapentaenoic acid levels, in controlling CMS in salmon after experimental infection with PMCV.ResultsHepatic steatosis associated with CMS was significantly reduced over the time course of the infection in fish fed the functional feeds. Significant differences in immune and inflammatory responses and pathology in heart tissue were found in fish fed the different dietary treatments over the course of the infection. Specifically, fish fed the functional feeds showed a milder and delayed inflammatory response and, consequently, less severity of heart lesions at earlier and later stages after infection with PMCV. Decreasing levels of phosphatidylinositol in cell membranes combined with the increased expression of genes related with T-cell signalling pathways revealed new interactions between dietary lipid composition and the immune response in fish during viral infection. Dietary histidine supplementation did not significantly affect immune responses or levels of heart lesions.ConclusionsCombined with the previous findings on HSMI, the results of the present study highlight the potential role of clinical nutrition in controlling inflammatory diseases in Atlantic salmon. In particular, dietary lipid content and fatty acid composition may have important immune-modulatory effects in Atlantic salmon that could be potentially beneficial in fish balancing the immune and tissue responses to viral infections.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-462) contains supplementary material, which is available to authorized users.

Cardiomyopathy syndrome in Atlantic salmon Salmo salar L.: A review of the current state of knowledge

“…Functional feeds are feeds that beyond their nutritional composition are formulated with health‐promoting features (Martinez‐Rubio et al., ). The health‐promoting function is typically gained either by altering the quantity or ratios of existing ingredients or by adding new ingredients.…”

“…A study published in 2014 concluded that salmon fed trial diets with lower lipid content (~18% versus ~31%), and higher Ω‐3/Ω‐6 ratio (PUFAs) (~4 to ~1.4) than in a reference diet, performed better after intramuscular challenge with PMCV. In one trial diet, histidine was added as this amino acid plays important roles as buffer and antioxidant in muscle cells (Martinez‐Rubio et al., ). The study concluded that lipid content and composition may have an immunomodulatory effect, resulting in a milder and delayed immune response after PMCV infection, and significant reduction in tissue damage during CMS outbreaks.…”

Digestibility of the defatted microalgae Nannochloropsis sp. and Desmodesmus sp. when fed to Atlantic salmon, Salmo salar

“…Furthermore, aberrations in lipid metabolism upon ingestion of plant oils may compromise fish health (Kjær et al., ; Todorčević et al., ). Recent research has also shown that salmon fed n ‐6 fatty acids are more susceptible to viral diseases (Martinez‐Rubio et al., , ). There is an urgent need to find novel feed ingredients, which are ideally not used directly as human food, for the aquafeed industry.…”

Increased dietary protein‐to‐lipid ratio improves survival during naturally occurring pancreas disease in Atlantic salmon, Salmo salar L.

“…The lower mortality and large reduction in runts among fish fed the test diet compared to those fed the control diet, is an important observation in this study. Previously, diets with reduced lipid content have been shown to reduce the inflammatory responses and associated heart lesions in salmon experimentally challenged with Atlantic salmon reovirus (ASRV) and piscine myocarditis virus (PMCV), that are associated with HSMI and CMS, respectively (Martinez‐Rubio et al., , ). In these studies, however, the reduced dietary lipid content was combined with increased levels of polyunsaturated fatty acids (PUFA), eicosapentaenoic acid (EPA) and phospholipids, and the dietary causative effects could not be separated.…”

“…The effectivity of some of these functional feeds has been reported in scientific studies. In line with this, low‐lipid diets containing high levels of specific fatty acids have been used as a potent tool to control HSMI and CMS in Atlantic salmon by modulating tissue fatty acid composition and eicosanoid production (Martinez‐Rubio et al., , ). Commercial available “PD feeds” are frequently used within the SAV3 endemic zone (Jansen et al., ), and these feeds are often formulated to have lower lipid and higher protein content than standard diets.…”