Transcriptome and functional responses to absence of astaxanthin in Atlantic salmon fed low marine diets

High content of carotenoids in tissues of salmonid species suggests possible functional importance, which has so far remained unclear. The objective of this study was to investigate the effect of astaxanthin on performance and gene expression of sea water adapted Atlantic salmon (Salmo salar) fed diets with low content of marine ingredients (7.5% fishmeal and 5% fish oil). Salmon with start weight 197 g were fed two diets with identical proximate composition except for the content of astaxanthin (<1 and 48 mg/kg, respectively) for 84 days. Absence of dietary astaxanthin caused significant transcriptome changes revealed with DNA microarray. The growth rate was not optimal for the two diet groups but was not affected by dietary astaxanthin concentration. Accumulation of lipid in the intestine and liver was found in salmon fed both diets, indicating malabsorption of lipid. Salmon fed the diet without astaxanthin had larger livers and higher fat content in liver due to accumulation of triglycerides, but the difference in fat content was not significant. Transcriptome responses in different organs suggested that lack of dietary astaxanthin may have functional consequences in salmon fed low marine diets. In the intestine of astaxanthin deprived salmon, decreased expression was observed in a suite of immune genes including genes of innate antiviral immunity, transporters and enzymes of glycan metabolism. Transcriptome responses in liver suggested effect of absence of astaxanthin on lipid metabolism and especially on increased biosynthesis of terpenoids and steroids and only minor effects on immune genes. The greatest transcriptome changes were observed in skeletal muscle in the absence of astaxanthin, with an up-regulation of immune-related genes (119) and multiple genes with well-established association with stress. The condition resembled a mild inflammation of the muscle. Small or moderate scale of gene expression changes were in concordance with equal growth performance of fish fed both diets, however their character may indicate potential risk of absence of dietary carotenoids.