Brain activity of Atlantic salmon (Salmo salar) following electrical stunning using various field strengths and pulse durations

The aim of this study was to investigate the effect of alternating current (a.c.) stunning on brain activity in Atlantic salmon (Salmo salar). Electroencephalography (EEG) was used to determine loss and return of consciousness following stunning. Three groups of salmon were stunned in seawater using 50 Hz sinusoidal a.c., with field strengths equal to 200, 50 and 25 V/m at current durations 1, 3 and 12 s. After stunning, visual evoked responses (VERs) were measured by EEG of the optic rectum. Results showed that all electrically stunned fish lost VERs, and that time to recovery of VERs was dependent on the combination of current duration and electric field strength. Hence, high voltage stunning, using 200 V/m in 1s resulted in a mean recovery time of VERs equal to 154 s, while low voltage stunning at 50-25 V/m in 3 and 12 s, the time to recovery was 288 and 212 s, respectively. These results show that electrical stunning can cause immediate loss of consciousness in fish, and can be applied as a stunning method prior to slaughter. (C) 2003 Elsevier Science B.V. All rights reserved.