Electrical stunning of rainbow trout (Oncorhynchus mykiss): factors that affect stun duration

Many present commercial methods of slaughtering fish for food cause stress and aversive behaviour, which could be considered inhumane. This is especially true for rainbow trout (Oncorhynchus mykiss), which are usually slaughtered by removal from water resulting in death by anoxia. In the context of fish farming, this slaughter method is becoming less acceptable both from a welfare perspective and in terms of providing consistent and potentially improved flesh quality characteristics. The increasing concern for the welfare of fish has led to research to improve the situation. The use of electricity at slaughter could offer a humane procedure for stunning and/or killing large numbers of small fish when carried out correctly. This paper separately investigates the importance of stun application time, frequency and current magnitude of a sinusoidal alternating current on the ability to stun and stun/kill rainbow trout. In particular, increasing current magnitude and current application time were both found to increase the time for which the animals were effectively stunned. Also, above a current magnitude threshold, the trout were killed by the application. Increasing the frequency of the current waveform decreased the stun duration, until a threshold frequency was reached, at which it is suggested that it may not be possible to stun trout with the current parameters used. All three parameters need to be considered to ensure a humane stun or stun/kill, but such applications may also have implications for quality attributes of the flesh. This investigation will assist in the design of a humane electrical slaughter device for rainbow trout.