Fishmeal (FM) and fish oil are becoming strategic ingredients for aquaculture feeds. In spite of considerable efforts to replace FM by alternative ingredients, problems with reduced feed intake and growth, as well as gut health issues (intestinal integrity and inflammation) are still common, associated with a lower palatability, digestibility and potential presence of anti-nutritional factors in these alternative raw materials. Similar problems have been successfully mitigated in terrestrial farmed animals using sensory additives containing umami compounds. These are amino acids that help an animal identify protein sources, which exert their effects through the activation of umami taste receptors both orally and extra-orally (e.g., along the gastrointestinal tract). The aim of this study was to test this concept in Atlantic salmon. A 16 weeks trial was performed with salmon juveniles (445±10g) reared in triplicate 850L tanks (19 fish/tank). Tested treatments were a high (20%) FM diet (HFM), a low (7.5%) FM (LFM) diet or a LFM diet supplemented with 0.4% of a prototype umami palatability enhancer (LFM+UPE). Results show a potential of the UPE to counteract the reduction in feed intake when 62.5% of FM was replaced by vegetable meals in salmon diets (Fig.1A). Although not significant, FCR was numerically lower in the LFM+UPE diet (Fig. 1B), which resulted in a tendentially higher growth (Fig. 1C). In addition, protein deposition rate and retention efficiency were improved in the LFM+UPE group (110.8g/fish and 37.5%), compared to the LFM (91.7g/fish and 32.6%) and HFM (92.2g/fish and 30.1%) treatments. Whole transcriptome sequencing (RNA-seq) of the anterior intestine was performed to characterize changes in its expression profile. Results revealed mechanisms possibly explaining the beneficial effects of the UPE, with several genes that compose the extracellular matrix, with likely effects on intestinal integrity, barrier function and/or cell proliferation, as well as amino acid transport genes, being significantly up-regulated. An RNA-seq analysis of liver tissue is ongoing, in an attempt to uncover mechanisms that could explain the trend for increased protein deposition and retention in the LFM+UPE treatment.