Electrical stunning and killing of lumpfish with commercial waterbath and dry stunners

Abstract

Lumpfish, ranging in size from 146-4200 g, were placed in an electric dry stunning unit head first and exposed to 50 Hz, 240 V AC for 0.5 or 1 s and thereafter 4.5 or 9 s of electricity, thus 5 and 10 s respectively. In seawater, lumpfish were exposed to an electric field equivalent of 4.6 Vrms/cm, 100 pps square AC, with 15% duty cycle for 1 s and thereafter 9 s. This to verify whether the animal is rendered unconscious prior to killing by a throat cut, immersion into cold brine (-14 to -18 °C) or hypoxic water supersaturated with CO2. Behaviour, heart (ECG) and brain (EEG) activity were monitored until the animal was classed as dead. Post the treatment, the internal temperature of the animal was measured by loggers placed into the brain and heart cavity. The electric potential across the brain was also measured. A preliminary evaluation of the EEG and ECG registrations in the individual fish showed that loss of consciousness may occur within 0.5 seconds stun as the fish displays epileptic insult, but unconsciousness could not be verified with EEG. A one-second stun did, however, result in verified unconsciousness both for dry and waterbath stunning. A prolonged electric exposure in combination with a cold brine resulted in permanent loss of consciousness until death, whereas a throat cut or exposure to water supersaturated with CO2 was insufficient and resulted in some fish recovering. Measurements of the electric potential difference across the brain showed that the electric field is dependent on the size of the fish for dry stunning, but not in water. Unconsciousness was reached as low as 2.8 V/cm Vpp across the brain, but with an average of 45 and 14 Vpp for dry and waterbath stunning, respectively. We conclude that electrical stunning in combination with cold brine is effective for humane stunning and killing of lumpfish.