Stunning challenges: Operational indicators flag failures, but neurological validation is needed to confirm stunning effectiveness in seabass and seabream

Humane slaughter in aquaculture depends on accurate assessments of insensibility, yet commonly used operational indicators remain poorly validated against neurological benchmarks. This study compared operational indicators such as the loss or recovery of equilibrium, 'eye-roll' reflex, and ventilation reflex with visually evoked responses (VERs) in European seabass ( Dicentrarchus labrax ) and gilthead seabream ( Sparus aurata ) subjected to anaesthetic immersion or in-water electrical stunning. Operational indicators consistently preceded or lagged behind VERs, risking misjudgment of fish sensibility. Notable species differences emerged, with seabass losing and recovering indicators faster than seabream, whose indicator sequences varied depending on stunning method. Among all indicators, the ventilation reflex aligned most closely with VERs in both species, suggesting it may be the most reliable operational proxy. Despite the increasing use of electrical stunning in commercial settings, rapid recovery times (within seconds to minutes) observed in most fish raise serious welfare concerns. These findings underscore the urgent need to improve and validate electrical stunning methods for seabass and seabream before they can be considered humane and are widely implemented. Until neurological tools are feasible for commercial use, thorough species- and method-specific validation of operational indicators remains essential for safeguarding fish welfare. • Operational indicators mismatched neurophysiological sensibility benchmarks. • Ventilatory reflexes aligned closest with VERs in seabass and seabream. • Species-specific differences found in sensibility indicator timing and sequence. • Rapid recovery following electrical stunning poses welfare risks. • Neurophysiological validation of indicators and stunning methods is essential.