FIRST STEPS TOWARD NEW INDICATORS OF UNCONSIOUSNESS DURING SHRIMP HARVEST ON FARM?

Introduction

In terrestrial animals, many indicators of unconsciousness coexist, recognized by the scientific community, some of which are used routinely to limit pain and suffering during slaughter. These indicators may vary depending on the stunning method (captive bolt or electrical stunning). Currently, shrimps Penaeus vanamei are primarily slaughtered by thermal shock, although electrical stunning is generating increasing interest. To date, no reliable indicator of unconsciousness has been established in the scientific literature, with the few publications on the subject presenting contradictory results.

Materials and Methods

Development of new indicators and a scoring system

We developed three indicators to assess shrimp reactivity during and after slaughter: eye contact, mouthpart contact, and uropod pinching. Five types of reactions (as opposed to no reaction) to these indicators were recorded:

1. Spontaneous movements present before any contact with the animal;

2. Movements of the locomotor appendages (pleopods and pereiopods);

3. Pleopod movements;

4. Pereiopod movements;

5. Attempted escape (jumping).

Tests during harvest in American production ponds

Data were collected in 2023 and 2024, from 746 shrimps reared in Central America, of small size (approximately 9 g) and large size (approximately 20 g). The indicators were assessed in shrimps: (i) immediately after stunning, (ii) after the ice slurry bath (at different temperatures and durations), or (iii) after the combination of both treatments (no data are available for large shrimps that had previously been stunned). Analyses were performed using a binomial model.

Results and discussion

The percentage of reactions varied according to the indicator, shrimp size, and slaughter method. Overall, the proportion of reactions versus no reaction differed from chance (Figure 1). Joint locomotor appendage movements, as well as pereiopod movements alone, were more frequent than other reaction types, regardless of shrimp size.

Immediately after stunning, fewer small shrimps reacted when their eyes were touched compared to after an ice slurry bath. No difference in reaction type was observed according to shrimp size.

With prior stunning and after the ice water bath, the number of small shrimps showing a reaction was lower than expected under a random distribution. Without prior stunning, the number of individuals showing a reaction was equivalent (small shrimps) or higher (large shrimps) than expected under a random distribution. The percentage of reactivity was lower in small shrimps when stunning preceded the bath.

Regarding the effect of ice temperature and immersion duration, reactivity decreased for small-sized individuals according to temperature and regardless of the indicator (for large shrimps, this phenomenon was only observed upon mouthpart contact).

Reactivity upon mouthpart contact decreased with immersion duration in ice water at constant temperature, for small shrimps (Figure 2).

Conclusion

The indicators used effectively assess reactivity and are quick and easy to implement during shrimp harvest. The observed reactions raise questions: are they voluntary movements? Indiquent-elles une douleur ?

Many shrimps remain reactive after slaughter, suggesting the need to improve current methods and to take their size into account in slaughter procedures.

Figure 1. Proportions of reactive and non-reactive individuals, according to the indicators tested, slaughter methods, and individual size, compared to a random proportion (N = 746)

Figure 2. Binomial linear models predicting the reactivity of small-sized shrimps according to immersion duration in the ice water bath at constant temperature (N = 54)

References

Browning, H., Burn, C., Schnell, A. K., Crump, A., & Birch, J. (2025). Animal welfare risks from commercial practices involving cephalopod molluscs and decapod crustaceans. Animal Welfare, 34, e24

Neil, D. M., Putyora, E., & Albalat, A. (2024). Towards the humane slaughter of decapod crustaceans: identifying the most effective indicators of insensibility following electrical stunning. Frontiers in Animal Science, 5, 1378350.

Weineck, K., Ray, A. J., Fleckenstein, L. J., Medley, M., Dzubuk, N., Piana, E., & Cooper, R. L. (2018). Physiological changes as a measure of crustacean welfare under different standardized stunning techniques: Cooling and electroshock. Animals, 8(9), 158.