Electric stunning of trout: power reduction using a two-stage stun

Electrical stunning in water using a high frequency (1000 Hz) power source is a humane and practical method for killing trout, which results in damage free carcasses. However, the electrical power requirement can be high, particularly with high conductivity water. The equipment needed for the high frequency power supply significantly adds to the capital cost of the equipment and can make such equipment impractical, particularly for use in high conductivity water. A two-stage approach to stunning has been demonstrated which reduces the electrical power required by over 80%. The approach is based on the observation that the electric field strength needed to induce rapid insensibility is greater than the electric field strength required to maintain stunned fish in a state of insensibility until they are beyond the point of recovery. It is further proposed that since the electric field required for the prolonged second stage is quite low, it might be possible to use a 50 Hz power source without causing carcass damage.