The effects of electrical stunning on the nervous activity and physiological stress response of a commercially important decapod crustacean, the brown crab Cancer pagurus L.

Abstract

Increasing attention is being paid to the welfare of decapod crustaceans. Legislation exists for their humane slaughter in several countries and this is being debated in others. Electrical stunning may have potential for humane slaughter of crustaceans in some circumstances, although scientific data on the effectiveness of electrical stunning when applied to various species are limited. Assessment criteria for effective stunning have so far been based mainly on behavioural assessments, but these do not always reflect neural insensibility. In this study direct recordings of neural activity, both centrally and peripherally, have been used to provide more direct measures of the state of sensibility. We have also examined whether electrical stunning acts as a physiological stressor, using measures of haemolymph L-lactate. Experiments were performed on a commercially important decapod species, the brown crab Cancer pagurus L. Spontaneous activity within the CNS was arrested by electrical stunning, which is an indication of loss of sensibility. There were also specific effects on the peripheral nervous system, with loss of responsiveness to sensory stimulation, rendering the animals unresponsive to external stimuli, and a failure of motor activation. All these effects were apparent immediately after a 10s stun, and persisted for as long as tested (4h) indicating that the animals were also killed by the procedure. No autotomy of limbs occurred. Haemolymph L-lactate was found to be no greater following electrical stunning than after handling and sampling alone, and both were significantly lower than values reached in a range of environmental and commercial situations. For all these reasons we find that electrical stunning may meet criteria for humane slaughter of C. pagurus.

Meta‐analytic assessment of physiological markers for decapod crustacean welfare

“…It is possible that single studies can inflate the overall influence of the stressor on the final result. For example, electro‐stunning was only presented in one study (Neil et al., 2022) and had one effect size calculated, but it was among the most influential stressors according to our model outputs (Table 5). The two most impactful stressors, trawling and emersion were represented by three and 31 studies, respectively.…”

Towards the humane slaughter of decapod crustaceans: identifying the most effective indicators of insensibility following electrical stunning

“…The methodologies used to electrically stun the C. maenas crabs and the H. gammarus lobsters, and to make neurological recordings, are here summarised and were the same as reported by Albalat et al (2022) and Neil et al (2022), where more detailed descriptions can be found.…”

“…This would allow time to take a blood or tissue sample, if required for biological analysis, or for an appropriate procedure for humane slaughter to be applied while the animal is in an insensible state (the concept of the 'stun-to-kill' time). In our previous study of brown crabs (Cancer pagurus) (Neil et al, 2022), lack of either nerve activity or behavioural responses at 4 h after stunning was taken to indicate that the crabs were also killed by this procedure, and this was corroborated by holding intact, electrically-stunned crabs for 24 h, and finding no signs of life. Other findings suggest that some caution needs to be applied to this interpretation.…”

“…More recently, Kells et al (2023) recorded global neural activity from superficially placed electrodes placed anteriorly and posteriorly on the spiny lobster Jasus edwardsii and the crayfish Paranephrops zealandicus. In our laboratory we have previously used the methods of selective extracellular recording described here to record from the central, sensory and motor systems of the crab Cancer pagurus (Neil et al, 2022) and the Norway lobster Nephrops norvegicus (Albalat et al, 2022). Taken together with the results of the present study on Carcinus maenas and Homarus gammarus, there is now available data for a number of crabs, lobsters and crayfish, which also encompass a range of sizes (body weights from around 50 g up to 1 kg) (Table 1).…”

“…However, until such reliable indicators of insensibility are identified it is necessary to continue performing laboratory studies directly on the nervous system to confirm that the stunning protocol meets the criteria for humane slaughter. By its nature the methodology for measuring neuronal activity can be invasive, but this is justified in a set of limited scientific trials aimed at identifying unambiguously the effectiveness of electrical stunning procedures in producing a state of insensibility (Albalat et al, 2022;Neil et al, 2022). These neuronal criteria can serve as a reference to confirm whether more convenient, yet less intrusive, physiological measures (e.g.…”