Document type : article published in The Fish Site
Author: C. Graig Lutz
Preview: The UK supermarket chain Tesco has recently launched a new crustacean welfare policy with a particular focus on decapod crustaceans such as lobsters, crabs and shrimp. New supply chain requirements include, among other things, electrical stunning of farmed shrimp post-harvest. Additionally, the chain will no longer sell any live decapods, such as lobsters or crabs, in its stores or online. These changes are the result of a growing number of concerns that, contrary to long-held conventional wisdom, some crustaceans may actually be sentient. But a number of pertinent questions remain unanswered.
Decapod sentience?
(...) The presence of sentience, on some level, is central to the concept of pain or suffering. In 2020 the International Association for the Study of Pain defined pain as "An unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage." Interestingly, the inclusion of the term "emotional" implies a conscious, affective component. Although other definitions of pain have been proposed, most of which also include both sensory and emotional components, perhaps the most appropriate definition for any evaluation of decapod crustaceans was offered by Wright (2011), who defined pain as "an unpleasant sensation that has evolved to motivate behaviour which avoids or minimises tissue damage, or promotes recovery." (...) Although the general consensus today is that most fishes are indeed sentient to some degree, the argument as to whether all decapods possess nervous systems capable of sentience has not been settled. (...) In an objective review of a number of studies, Elwood et al. (2017) pointed out that although the responses of decapods may be similar to those of vertebrates when subjected to certain noxious chemicals, definitive proof of such pain is not currently feasible. (...) Crump et al. provided a framework for evaluating sentience in decapods. They included eight "neural and cognitive behavioural" criteria. While astacid lobsters and crayfishes met only three of the eight criteria, the authors admitted that the case was weaker still for penaeid shrimps. (...) The best evidence for painful affect in animals is learned aversion to stimuli associated with noxious experience, and conditioned preference for contexts associated with relief from aversive consequences of noxious experience, as expressed in voluntary behavior. Such evidence is currently lacking for any invertebrate except octopus." Comstock provided an important caveat to generalised attributions of pain in decapods: "Some studies report pain avoidance behaviors in Dendrobranchiata (Penaeidae) shrimp, but further studies are needed to determine whether the chemicals used are acting as analgesics to relieve pain, or as soporifics to reduce overall alertness. If the latter, the most farmed shrimp species may not require the same level of protection as crabs, crayfish, and lobsters." Despite its controversy, many farms still employ eyestalk ablation.
Eyestalk ablation
Tesco's new crustacean welfare policy stipulates that 100% of shrimp broodstock used to produce farmed shrimp for it to sell must be ablation-free by 2026(Penaeus vannamei) or 2027(Penaeus monodon). Two other UK retailers, Marks & Spencer and Waitrose, have already ceased purchasing farmed shrimp from ablated broodstock. Leaving aside the as-yet unresolved biological and philosophical discussions over decapod sentience, let's consider the practice of eyestalk ablation in shrimp hatcheries throughout the world. The usefulness of unilateral (one side only) ablation to promote maturation and spawning in female penaeid shrimp was established more than 50 years ago (Idyll 1971). From my observations in several countries, ablated shrimp typically appear wholly unbothered within 30 minutes after the procedure, with little evidence of any long-term stress or discomfort. Nonetheless, certain protocols have been shown to completely eliminate even short-term adverse experiences associated with ablation. (...) However, as mentioned above, some sectors of the global shrimp marketplace are increasingly demanding the industry find alternatives to ablation, and researchers and industry have responded to the pressure. Zacarias et al. (2019) compared the reproductive performance and offspring quality of ablated and non-ablated female L. vannamei under conditions similar to those of a commercial hatchery. Mating success and egg/larvae production were lower for non-ablated females, but so was their mortality over time. When non-ablated females spawned successfully, their fecundity was significantly higher than that of their ablated counterparts. Production of eggs and nauplii per broodstock tank was 44 percent and 45 percent lower, respectively, for non-ablated females, which would translate to significantly higher capital and operating costs for a hatchery using non-ablated broodstock. The authors proposed that certain adjustments in management and husbandry could offset some of these impacts, as might the longer lifespan of non-ablated females. Additionally, the commercial cooperator in the study indicated improvements had been observed in mating success of non-ablated females over successive generations, possibly as a result of domestication selection. (...) The higher resilience and survival demonstrated by offspring of non-ablated females might also serve to partially offset their reduced productivity under hatchery conditions. And, contrary to the findings of other studies with penaeid shrimps, Menezes et al. (2019) reported that non-ablated P. vannamei broodstock actually exhibited significantly higher mating frequency, spawning frequency, survival, number of eggs per female and number of nauplii per female than ablated females. (...)
