*Animal Law Journal has set the basis for this question for anyone to consider.

This article considers whether the Animal Welfare Act 2006 should be extended to include decapods (an order of crustaceans which includes shrimps, crabs, and lobsters). Whether or not decapods feel pain is an important area in animal welfare research. The sheer number of decapods used within the food industry and the treatment which they are subject to should indicate that welfare should be improved if evidence of pain is found. Decapods are not classed as a ‘protected animal’ under s.2 of the Act. However, under s.1(3)(a) the definition of an animal can be extended to include invertebrates of any description, including decapods, if it can be satisfactorily proven on the basis of scientific evidence that the animal is capable of suffering.

There are many methods of slaughter in place which the EU’s Animal Health and Welfare Scientific Panel have declared as being inhumane [1]. This includes live boiling, chilling in the freezer prior to live boiling and live carving and dismemberment. It has been estimated that a crab which is boiled alive is able to sense heat for at least three minutes [2]. Keeping live lobsters on the ice has been banned in both Switzerland and Italy as it is shown to ineffective as an anesthesia, and simply paralyses the lobster [3]. If slaughter methods such as these were used on vertebrates such as pigs and cows, there would be a public outcry.

Therefore, the first issue to consider is whether decapods are capable of experiencing suffering.  As suffering and the ability to feel pain is an internal experience, it can be difficult to prove that any animal is capable of suffering, including those already within the scope of the Act. Therefore, scientists seek to show that decapods are capable of feeling pain due to their nervous systems and physiological and neurochemical mechanisms and that they also give a behavioural indication that they feel pain.

The key question when researching pain in animals is whether the animal’s response to a harmful stimulus, known as a nociception, entails pain. However, this response must be examined to determine whether or not it is because the stimulus is a source of pain, or if it is simply a reflex response.


Nociceptors and a central nervous system
Nociceptors: a sensory receptor for painful stimuli

Crustaceans possess nociceptors which are grouped into cuticular extensions of the shell, known as sensilla. Their central nervous system is made up of a double ventral nerve cord linking a string of ganglia. The largest of these ganglia are found at the head and functions as the brain [4]. Although a crustaceans’ brain is small in comparison to a vertebrate brain, this does not mean that they don’t experience pain [5].


Effects of analgesics 
Analgesics: a drug to relieve pain

There have been studies to show that the effects of opioid analgesics are similar to those produced in vertebrates. For example, in a study observing crabs, the animals were given an electric shock which resulted in them behaving defensively. It was found that injections of morphine reduced electric shock sensitivity [6]. In a second study, the fear response of running was lessened by morphine [7]. This response to morphine indicates the possibility that crustaceans possess the ability to regulate pain.


Cognitive ability

Animals with good cognitive skills are assumed to be more likely to experience pain [8]. It has been argued that hermit crabs “show an excellent ability to gather, manipulate and use information from multiple sources, indicating a higher cognitive ability than generally recognised [9].” Crustaceans gather information about new shells and integrate that with the information they already have about their current shell, allowing them to decide between the two.


Avoidance learning

Avoidance learning is a reflex response to a harmful stimulus in order to be protected from it. A common example seen within humans is when our hands touch a hot surface, we involuntarily withdraw it in order to avoid the pain. Through this experience of pain, animals are able to learn to avoid the same stimulus in the future, suggesting that the ability to feel pain is necessary for this to occur. Multiple studies have been able to demonstrate that decapods use avoidance learning; in one study crayfish learned to associate a light signal with a shock, and to avoid the shock by walking to the other end of the box; [10] and in a second study shore crabs were less likely to enter one of two dark shelters if they had previously received a shock there [11].


The Precautionary Principle

Scientists recognise that absolute scientific certainty does not exist; much of their work involves trying to gain more certainty. If this is so, how should we treat an animal of whose mental abilities we know something about, but are uncertain? This is where a precautionary principle is adopted. The precautionary principle “rejects science as the notion that there is an absolute guide for the policy maker, and embodies the notion that there is uncertainty regarding the potential impact of an activity, rather than await certainty, regulators should act in anticipation of possible harm to ensure that this harm does not occur [12].” For many centuries the law followed an approach which exploited non-human animals as they were thought to lack basic mental ability, such as rationality and consciousness. However, now there is clear evidence that animals do not lack these things, including decapods. This is where we should apply the precautionary principle in light of a decapods’ ability to suffer. The precautionary principle has already been applied to extend the scope of animal protection legislation to include fish and some invertebrates, such as cephalopods, [13] which indicates it is very possible to extend the legislation to cover decapods. Where there is a doubt that decapods do not feel pain, we should err on the cautious side when some evidence of suffering exists.

An example of the precautionary principle in practice is the reasoning that led to the 2010 EU directive on the protection of animals used for scientific purposes, in which policymakers acted on the expert advice of animal welfare scientists. They proposed that “inclusion of any invertebrate species… should only occur on the basis of sound scientific evidence as to their sentience and the ability to feel pain, as assessed by a Scientific Committee of experts…[14]” Following the reports of the working group, the Animal Health and Welfare panel of the European Food Standards Agency was invited to give an opinion, which included a recommendation as to which vertebrates should be included.

The case that decapods are both capable of feeling pain and experiencing suffering is convincing. Even if the law were to demand that more scientific proof is needed to determine that they suffer, the precautionary approach should be adopted within the Act. This will protect decapods if more scientific evidence is found to show their ability to experience pain. Without the inclusion of decapods within the scope of the Act, it is arguable that the law is inconsistent, as there is as much evidence to show that decapods experience pain as vertebrates.



[1] The EFSA Journal (2005) 292, 1-46 – Opinion on the “Aspects of the biology and welfare of animals used for experimental and other scientific purposes”.

[2]Roth, B. and Øines, S., 2010. Stunning and killing of edible crabs (Cancer pagurus), Animal Welfare, Volume 19, Number 3, August 2010, Universities Federation for Animal Welfare pg 287-294(8)

[3]Neil, D. and Thompson, J., 2012. “The stress induced by the Crustastun process in two commercially important decapod crustaceans: the edible brown Cancer pagurus and the European lobster Homarus gammarus” Institute of Biodiversity, Animal Health and Comparative Medicine at the School of Medical Veterinary and Life Sciences, University of Glasgow.

[4] Elwood, R.W., Barr, S. and Patterson, L, 2009 “Pain and stress in crustaceans?” Applied Animal Behaviour Science 118 (2009) 128-136

[5] Broom, D.M., 2007 “Cognitive ability and sentience: which aquatic animals should be protected?” Disease of Aquatic Organisms 75: 99-108

[6] Lozada, M., Romano, A., Maldonado, H., 1988 “Effects of morphine and naloxone on a defensive response of the crab Chasmagnathus granulatus.” Pharm. Biochem. Behav. 30, 635-640

[7] Maldonado, H., Romano, A., Lozada, M., 1989. “Opiate action on response level to danger stimulus in the crab Chasmagnathus granulatus.” Behav. Neurosci. 103, 1139-1143

[8] Dawkins, M.S., 2006 “Through animal eyes: what behaviour tells us.” Appl. Anim. Behav. Sci. 100, 4–10.

[9] Elwood, R.W., Barr, S. and Patterson, L, 2009 “Pain and stress in crustaceans?” Applied Animal Behaviour Science 118 (2009) 128-136

[10] Kawaia, N., Konob, R. and Sugimotob, S., 2004 “Avoidance learning in the crayfish (Procambarus clarkii) depends on the predatory imminence of the unconditioned stimulus: a behavior systems approach to learning in invertebrates.” Behavioural Brain Research. Volume 150, Issues 1–2, 2 April 2004, Pages 229–237

[11] Magee, B. and Elwood, R.W. 2013 “Shock avoidance by discrimination learning in the shore crab (Carcinus maenas) is consistent with a key criterion for pain.”

[12] Wise, M. S., 2002 “Drawing the Line” Perseus Book Groups pg 39

[13] Andrews, P. L. R. 2011 “Laboratory invertebrates: Only spineless, or spineless and painless?” ILAR Journal 52:121-125

[14] Technical Expert Working Group (TEWG) 2003, pg 6


One thought on “Should animal welfare legislation be extended to include decapods?*

  1. The literature cited here seems extremely selective. It excludes many scientific papers discuss problems in building a cases for crustacean pain. This recent review describes significantly more research, and is free to read.
    Diggles, B.K. 2018. Review of some scientific issues related to crustacean welfare. ICES Journal of Marine Science: fsy058. doi: 10.1093/icesjms/fsy058
    This post also oversimplifies the findings of some of the papers cited here. For instance, reference 10 (Kawai et al. — authors’ names are incorrect in citation) showed avoidance learning was highly variable and dependent on context.


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