Assessment of brain function during stunning and killing of channel catfish (Ictalurus punctatus)

Measurement of brain activity is a reliable method to determine loss of consciousness during the slaughter of terrestrial farm animals. In fish, the ability to obtain an electroencephalogram (EEG), even in unrestrained individuals, has enabled the assessment and optimization of stunning and killing methods in aquaculture. This study evaluated the effect of percussive and in-water electrical stunning in channel catfish ( Ictalurus punctatus ) using the loss of visual evoked responses (VERs) as indicator of loss of consciousness. Our results show that percussive stunning with a fish bonker effectively caused permanent disruption of normal brain function when applied correctly. However, there is a risk of mis-stuns, with 20 % of the catfish showing temporarily or permanently responsiveness after stunning ( i.e. presence of VERs). Exposure to an electric field strength of 13 V rms cm −1 and a current density of 1.3 A rms dm −2 for 1 s caused immediate but, in contrast to successful percussive stunning, transient loss of VERs. Extending the exposure time to 10 s using the same electrical parameters did not affect recovery based on VERs, nor did increasing the field strength to 24 V rms cm −1 and a current density to 2.1 A rms dm −2 using a 10 s exposure time. The recovery time was also unaffected by post-stun placement of fish in air or water. However, a 10 s shock with an electric field of 24 V rms cm −1 and a current density of 2.1 A rms dm −2 immediately followed by decapitation, prevented recovery in 70 % of the catfish with the remaining 30 % experiencing temporary recovery ( i.e. presence of VERs) for a few minutes. Our findings show that different stunning methods offer distinct advantages and limitations. Modifying the slaughter protocol in commercial catfish production, considering these methods, could significantly enhance the welfare of channel catfish during slaughter. • In-water electrical stunning can induce loss of consciousness in channel catfish. • Investigated field strengths and current densities had no effect on recovery time. • Recovery in air or water have no effect on time to recovery. • Electric stunning followed by decapitation prevented recovery in 70 % of the fish. • Percussive stunning can induce permanent loss of consciousness if done correctly.