A humane protocol for electro-stunning and killing of Nile tilapia in fresh water

Behavioural, neural and physiological parameters were scored after electro-stunning of Nile tilapia ( Oreochromis niloticus ) in three positions to an electric field in fresh water. An overall current density, 1.0 A rms /dm 2 , 50 Hz sinusoidal, applied for 1 s top-to-bottom in water (700 μS/cm), induced a general epileptiform insult on the EEG for 26 ± 10 s ( n = 24). The ECG revealed fibrillation for 9 ± 4 s in 15 out of 24 fish. To kill without recovery, the current was applied for 5 s, followed by chilling in ice water for 15 min. Killing of the stunned fish by gill-cutting instead of chilling is not recommended, as 2 out 4 tilapias responded 10 min post stun. When electricity was applied head-to-tail on tilapia ( n = 8), the overall current density could be reduced to 0.4 A rms /dm 2 , 50 Hz sinusoidal, to induce a general epileptiform insult, which lasted 27 ± 10 s. A pulsed square wave alternating current (overall density of 0.6 A rms /dm 2 , 133 Hz and 43% duty cycle) was applied for 1 s side-to-side on tilapia in water (650 μS/cm). This induced a general epileptiform insult for 51 ± 37 s ( n = 14). Fibrillation occurred for 16 ± 7 s ( n = 10). Free-swimming fish righted between 68 and 95 s ( n = 5) and between 438 and 1139 s ( n = 5) after 1 and 5 s electro-stunning, respectively. Our results show that protection of welfare of tilapia at slaughter can be obtained with electro-stunning followed by killing the stunned fish in ice water.