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The evaluation of new diet composition is commonly achieved by performing time-consuming growth trials, which may negatively impact the welfare of a large number of fish if the feed is not accepted. Instead, the fish's behavioural responses to a new diet composition can be used as a first step in the evaluation of new diet composition. The taste acceptance of a new diet by Arctic charr ( Salvelinus alpinus ) was evaluated over 16 days based on the self-selection of a test diet and a control diet. The test diet contained ingredients from the nutrient-enriched Baltic Sea, and it is hoped that this diet can contribute nutrients to the nutrient-poor waters in northern Sweden in which Arctic charr are farmed. The main ingredients in the test feed were blue mussel meat ( Mytilus edulis ), meat from sprat ( Sprattus sprattus ) and herring ( Clupea harengus ), baker's yeast ( Saccharomyces cerevisiae ), fish oil and regionally produced rapeseed oil. Individual fish ( n = 15) were allowed to choose between abundances of both the test diet and a fishmeal based control diet that mimicked a standard feed for Arctic charr. After only a few days, the fish demonstrated a significant preference for the Baltic Sea test feed. These results may depend on betaine, which was found at concentrations that were four times higher in the test feed than in the control feed. Betaine is a known attractant for many fish species and is abundant in marine animals, such as mussels. Thus, the test diet can be evaluated further without additional taste stimulants before the new feed formula can be used commercially to ensure fish welfare, the product quality and the economic feasibility of the new formula. [ABSTRACT FROM AUTHOR]