Ikejime is a technique used to kill fish by inserting a spike into the brain, which can be performed manually or mechanically. This technique originated in Japan and aims to reduce stress and prevent uncontrolled muscle contractions after the catch, thereby preserving the quality of the meat and prolonging its freshness. This not only preserves the original flavour and texture of the fish, but also creates a rich “umami” taste. In this study, the proximate composition, amino acid profile and fatty acid composition with the degree of their oxidation were compared in farmed sea bass (Dicentrarchus labrax) killed by cold water asphyxiation after capture and the samples bled during capture using the Ikejime technique. No significant difference was found between the samples in proximate and fatty acid composition. Lipid oxidation, measured by the tiobarbituric acid test, showed similar results with no significant difference: 0.62 ± 0.01 µmol malondialdehyde (MA)/100g in the sea bass killed by cold water asphyxiation, and 0.76 ± 0.01 µmol MA/100g in the sea bass killed by Ikejime. The lower levels of ASP, HIS, GABA, MET and LYS found in Ikejime-treated sea bass indicate lower stress and delayed proteolysis, which enhances the oxidative and microbial stability of fish killed by this technique. While the immediate umami flavour can be milder, the flavour improves with a short period of maturation, making Ikejime fish ideal for high-quality, well-matured seafood products.