To avoid severe discomfort in fish at slaughter or killing, it is key to protect these animals by stunning them , i.e. rendering fish unconscious and insensible first. This is a general provision in the Council Regulation (EC) No. 1099/2009. This provision is met when stunning induces an immediate loss of consciousness and sensibility in fish, which lasts until death.
It is known that most farmed fish are produced in Asia. Since 2014, Vietnam has been the third exporter of farmed fish. Vietnam has become by far the world’s leading producer and exporter of farmed pangasius. We, therefore, selected pangasius in our experiments.
In our experiments, we aimed to establish the specifications for two electrical stunning methods for farmed pangasius, i.e. in water and after dewatering. We also assessed whether cutting the ventral aorta could prevent recovery of the stunned animals.
Electrical stunning in water. For electrical stunning in water, a field strength of 7.2 V/cm (50 Hz ac) was applied in (140-200 µS/cm) to pass sufficient current through the brains of each fish , using EEG registrations and behavioural observations. Individual pangasius were exposed to a one-second stun to establish the conditions for an immediate loss of consciousness and sensibility . Cutting the ventral aorta after an exposure of 20 s to the electricity resulted in death in the individual fish without recovery, using EEGs and behavioural observations .
Electrical stunning after dewatering (Fig. 1). Our data showed that 200 V 50 Hz ac across the electrodes for 1 second is sufficient for an immediate stun in pangasius, using EEG registrations and behavioural observations . When the fish were exposed for 15 s to the electricity followed by cutting the ventral aorta, an immediate loss of consciousness and sensibility was achieved without recovery, using EEGs and behavioural observations.
To conclude, our data show that both electrical stunning in water and after dewatering can serve as an effective stunning method for farmed pangasius. Recovery of the stunned animals can be prevented by cutting the ventral aorta.