Abstract

The inclusion of plant meals in diets of farmed Atlantic salmon can elicit inflammatory responses in the distal intestine (DI). For the present work, fish were fed a standard fish meal (FM) diet or a diet with partial replacement of FM with solvent-extracted camelina meal (CM) (8, 16, or 24 % CM inclusion) during a 16-week feeding trial. A significant decrease in growth performance was seen in fish fed all CM inclusion diets (Hixson et al. in Aquacult Nutr 22:615–630, 2016). A 4x44K oligonucleotide microarray experiment was carried out and significance analysis of microarrays (SAM) and rank products (RP) methods were used to identify differentially expressed genes between the DIs of fish fed the 24 % CM diet and those fed the FM diet. Twelve features representing six known transcripts and two unknowns were identified as CM responsive by both SAM and RP. The six known transcripts (including thioredoxin and ependymin), in addition to tgfb, mmp13, and GILT, were studied using qPCR with RNA templates from all four experimental diet groups. All six microarray-identified genes were confirmed to be CM responsive, as was tgfb and mmp13. Histopathological analyses identified signs of inflammation in the DI of salmon fed CM-containing diets, including lamina propria and sub-epithelial mucosa thickening, infiltration of eosinophilic granule cells, increased goblet cells and decreased enterocyte vacuolization. All of these were significantly altered in 24 % CM compared to all other diets, with the latter two also altered in 16 % CM compared with 8 % CM and control diet groups. Significant correlation was seen between histological parameters as well as between five of the qPCR analyzed genes and histological parameters. These molecular biomarkers of inflammation arising from long-term dietary CM exposure will be useful in the development of CM-containing diets that do not have deleterious effects on salmon growth or physiology.Electronic supplementary materialThe online version of this article (doi:10.1007/s10126-016-9704-x) contains supplementary material, which is available to authorized users.

Highlights

  • Fish products are an important component of many human diets, and the demand for marine products is increasing as the global population has grown past seven billion (FAO 2009)

  • The growth performance of the fish involved in this feeding trial was previously reported in Hixson et al (2016), and the growth performance of fish fed the control diet (0CM) was reported in Hixson et al (2014); the results for the subset of diets that were used in this study are briefly described and reported as they are directly pertinent to the current study

  • The visceral somatic index (VSI) of fish fed the camelina meal (CM)-containing diets increased when compared to the fish fed the control diet (p = 0.001) but there was no significant difference between the CM diet groups

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Summary

Introduction

Fish products are an important component of many human diets, and the demand for marine products is increasing as the global population has grown past seven billion (FAO 2009). Plant-based products are not typically part of the diet of wild Atlantic salmon, and the supplementation of feeds for Atlantic salmon with plant meals (PM) may lead to inflammation of the distal intestine (DI) (enteritis) (Chikwati et al 2013; Marjara et al 2012; Moldal et al 2014; Overland et al 2009; Sahlmann et al 2013). In Atlantic salmon, the hindgut is the main site of amino acid absorption in the digestive tract and, as such, any loss of function that may be caused by inflammation can lead to a decline in the growth performance of the fish (Lokka et al 2013; Sire et al 1981)

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