Long-chain omega-3 fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are health beneficial lipids found in high concentration in pelagic fishes, including Atlantic mackerel. While EPA and DHA are sensitive to oxidative degradation during fish storage and processing, post-mortem degradation in the first hours following fish death is poorly documented. In this study, we stored fish at two temperatures (2-4°C and 18-20°C) and monitored EPA+DHA content in dorsal fillet 6, 12 and 24 hours after fish death and after cooking (grill or steam). Storage duration was the most influencing factor, and EPA+DHA loss was faster at 18-20°C. Six hours after fish death, and regardless of storage temperature EPA+DHA content decreased by 1.3±1.3 mg.g-1 (9.6±9.5% of the initial content). EPA+DHA losses were highly variable among individuals, probably because of other sources of variability (e.g., sampling position). Handling between fishing operation and deep-frozen storage should be as short and as cool as possible to preserve EPA+DHA and for food safety. Regarding cooking, both EPA+DHA and mono-unsaturated fatty acids increased in grilled fillets.