Digesta and Plasma Metabolomics of Rainbow Trout Strains with Varied Tolerance of Plant-Based Diets Highlights Potential for Non-Lethal Assessments of Enteritis Development

The replacement of fishmeal in aquafeeds is essential to the sustainability of aquaculture. Besides the procurement of alternative protein sources, fish can also be selected for better performance on plant-based alternative diets. Rainbow trout (<em>Oncorhynchus mykiss</em>) is one such species in which the strain ARS-<em>Sel</em>has been selected for higher growth and enhanced utilization when fed soy-based diets. The aim of this study was to compare fish growth, and plasma and digesta metabolomes between the ARS-<em>Sel</em>and two commercial strains (CS-1 and CS-2), when fed a plant-protein diet (PM) and a fishmeal-based diet (FM) and correlate them with the onset of enteritis. An NMR-metabolomics approach was taken to assess plasma and digesta metabolite profiles. Diet and strain showed significant effects on fish growth, with the ARS-<em>Sel</em>fish receiving the PM diet reaching the highest final weight at sampling. Multivariate analysis revealed differences between plasma metabolite profiles of ARS-<em>Sel</em>and CS (CS-1 considered together with CS-2) PM-fed groups in the early stages of the enteritis development, which was confirmed by a histological approach. In digesta, no differences were observed between groups. As reported in previous studies the ARS-<em>Sel</em>strain performed better than the commercial strains when fed the PM diet.