Behavioural and neurological profiles after electrical stunning and cold shock in Pacific whiteleg shrimp (Penaeus vannamei) to inform humane slaughter

Abstract

Worldwide shrimp aquaculture is dominated by Pacific whiteleg shrimp (Penaeus vannamei). While legislative protection is limited, there is increasing interest in developing humane slaughter practices. Current commercial methods include cold shock (CS) using ice slurry, followed by placing animals in ice. To assess whether a prior electrical stun (ES) would be more humane, we compared in-water ES followed by CS vs CS at different temperatures (−2.5 to +5 °C). Effectiveness was assessed by examining behavioural responses and electrophysiological recordings from the brain (supraoesophageal ganglion). Behaviourally, CS animals displayed a series of tail flips after ice slurry immersion, whereas ES animals displayed one vigorous tail flip upon first contact. However, after subsequent CS immersion, a subset of ES animals responded with further tail flips, which was most prevalent in animals stunned at lower voltages for a shorter duration (2–2.5 V cm1 for 5 s). By contrast, animals exposed to higher voltages for a longer duration (2.5–3 V cm−1 for 20 s) were less likely to tail flip after CS immersion. Electrophysiological recordings between these two groups were substantially different and insensibility could only be confirmed (total power, Ptot <10%) in the animals that did not respond to subsequent CS. Additionally, reducing the ice slurry temperature to below 0 °C for CS animals reduced the time to insensibility (Ptot <10%). Our results show that the absence of tail flipping after cold exposure is aligned with neurological insensibility in P. vannamei after in-water ES and highlights the importance of CS after ES.