Understanding how different pre-slaughter and slaughter procedures modulate physiological and neurochemical pathways in European sea bass (Dicentrarchus labrax) remains essential for welfare-oriented aquaculture. This study comparatively evaluated six procedures: clove oil and 2-phenoxyethanol anaesthesia, percussive stunning, asphyxiation in ice slurry or on solid ice, and clove oil anaesthesia followed by ice slurry, using plasma glucose and whole-brain monoaminergic indices as integrative physiological response indicators. Ninety-six fish were analysed. Ice-based asphyxiation and 2-phenoxyethanol exposure were associated with the highest plasma glucose concentrations, whereas clove oil and percussive stunning showed comparatively lower values. Dopaminergic and serotonergic turnover ratios (DOPAC/DA; 5-HIAA/5-HT) increased sharply under ice and 2-phenoxyethanol treatments, indicating increased monoaminergic activity under these procedures. Multivariate analyses (MANOVA, PCA) distinguished anaesthetic-based treatments from ice-based methods according to their combined neurochemical profiles. Although correlations between glucose and monoaminergic indices were modest, they were statistically significant and consistent with coordinated metabolic–neurochemical adjustments. Overall, DOPAC/DA and 5-HIAA/5-HT ratios emerged as sensitive and mechanistic biomarkers capable of differentiating slaughter procedures according to their relative physiological impact. These findings support the integration of metabolic and neurochemical indicators in welfare assessment and may contribute to evidence-based refinement of humane slaughter protocols in Mediterranean aquaculture systems.
Tsopelakos et al. (Sat,) studied this question.