Depth and season‐related variability in fatty acid composition and lipid nutritional quality indices of farmed <i>Mytilus galloprovincialis</i>

BACKGROUND: Lipid quality is one of the most important indicators of the nutritional value of farmed mussels. In open-coastal environments, factors such as cultivation depth and seasonal changes affect lipid dynamics, but their combined effects on lipid quality remain unclear. This study examined how depth and season influence fatty acids and lipid quality in farmed Mytilus galloprovincialis at 1 m and 10 m depths over a year. RESULTS: Across depths, 37 fatty acids were identified, with polyunsaturated fatty acids (PUFAs) dominating the lipid fraction (48.63% at 1 m; 48.88% at 10 m). Long-chain n-3 PUFAs, particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), exhibited narrower and more consistent seasonal patterns at 10 m than at 1 m. Lipid quality indices remained within favorable ranges throughout the year. At 1 m, Index of Atherogenicity (IA) and Index of Thrombogenicity (TI) increased sharply in autumn, reaching approximately 0.79 and 0.30, but changes at 10 m were gradual. Flesh Lipid Quality (FLQ), Polyene Index (PI), unsaturation index (UI), and Health Promoting Index (HPI) displayed wider seasonal amplitudes at 1 m but more constrained ranges at 10 m. CONCLUSION: This study indicates that seasonal variations primarily influence fatty acid composition, with cultivation depth playing a secondary role. Depth mainly impacts the stability of lipid quality indices rather than causing uniform changes in individual fatty acids. These results indicate that depth management could help promote product standardization in open-coastal mussel farming. © 2026 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.