Impact of Nannochloropsis gaditana diet on Sparus aurata metabolism by using an omics approach

Microalgae are recognised today as a promising functional feed and their inclusion in aquaculture feeding represents a sustainable environment-friendly alternative. One of the more promising microalgae in terms of nutritional content and easily integrable in biorefineries is Nannochloropsis gaditana. The main objective was to perform a metabolomic untargeted profiling on Sparus aurata fillets to distinct following feeding trails performed: diet without microalgae (Control) and four different diets with N. gaditana either with 5% raw microalgae or with 5% hydrolysed microalgae, from inorganic nutrient or biorefinery. The fish fillets were analysed by liquid chromatography coupled with high- resolution mass spectrometry (LC-HRMS, Q-Exactive – CD). Applying omics software, 320 molecules were identified. The majority of recognized compounds belong to the class of amino acids and their metabolites, and products of lipid metabolism. The presence of various lipids, products of glycolysis and pyruvate metabolism, principal mono/ oligosaccharides, nucleotides and nucleosides, and vitamins were confirmed as well. The content of some amino acids and their metabolites revealed significant differences between experimental diets. Specifically, in the muscle of fish fed with hydrolysed microalgae, there was an increase in essential amino acids: valine, methionine and arginine. These compounds can be used as potential markers of higher nutritional quality of diets with hydrolysed microalgae. The muscle of fish raised with the experimental diets also contains the highest amounts of glutathione and carnosine. The incorporation of the microalgae in the fish diet had a significant and progressive impact on the fish metabolome profile. The metabolites modulated by microalgae meal were involved in protein, lipids and energy metabolism. The findings provide new insights into how the dietary food metabolome affects fish metabolism.