Updated project metadata. Understanding the molecular mechanisms of feed efficiency is an important step toward sustainability of salmonids aquaculture. In this study, the liver and white muscle proteomes of efficient (EFF) and inefficient (INEFF) Chinook salmon (Oncorhynchus tshawytscha) farmed in sea water were investigated by liquid chromatography-tandem mass spectrometry (LC-MS/MS) approach. In total, 2,746 liver and 702 white muscle quantified proteins were compared between 21 EFF and 22 INEFF fish. Protein synthesis was enriched in both liver and white muscle of the EFF group while conversely, pathways related to protein degradation (amino acid catabolism and proteolysis, respectively) were the most affected processes in the liver and white muscle of INEFF fish. The SOM in the INEFF group was significantly higher than EFF fish showing INEFF fish probably was the dominant group. The INEFF group (dominant) suffered stress and shifted to consume energy through protein catabolism. As the first study, the results provide a preliminary picture of the fundamental molecular landscape of feed efficiency in Chinook salmon farmed in sea water