Pain in Crustaceans?

Do a Google news search for “lobster” and “pain” and you will come up with a list of conflicting news articles such as “Lobsters and Crabs Feel Pain, Study Shows” and “Scientists Say Lobsters Feel No Pain”. Its a hot debate, the research and reporting on crustacean nociception and pain is mixed and complex, there just is no simple scientific consensus on the issue. While researching the subject I stumbled across this blog post in which the author rightly debunks the myth that lobsters scream when boiled, the sound is actually hot air escaping through their carapace. But the author then asserts that lobsters and other crustaceans also simply do not have the necessary “nerve pathways and brain regions” to feel pain. The author goes on to say that “…they don’t have a real brain at all, for that matter. In other words, no brain, no pain”. While there is legitimate contention about the degree to which crustaceans are sentient or can feel pain, the idea that lobsters (and other crustaceans) do not posses a brain or endogenous opioid receptors is simply false. I’m not sure where the author was getting their information, perhaps it was this 2005 CNN article, which uses the “No brain, no pain” phrasing, about a report on lobsters in which scientists at the University of Oslo state “it is unlikely that they can feel pain.” But it was far from conclusive, the scientists themselves wrote near the end of their report,

“Still, it is not clear if the lobster can feel pain…we may be mistaken in assuming that invertebrates have a reduced capacity to experience suffering. Suffering is a private experience, or a negative mental state that cannot be measured directly. The responses of invertebrates to noxious conditions are often strikingly similar to those of vertebrates. Several experimental studies have shown that invertebrates such as cockroaches, flies and slugs have short and long-term memory, have ability of spatial and social learning, perform appropriately on preference tests, and may exhibit behavioural and physiological responses indicative of pain. The similarity of these responses to those of vertebrates may indicate a level of consciousness or suffering that is normally not attributed to invertebrates.” and added “there is apparently a paucity of exact knowledge on sentience in crustaceans, and more research is needed”

In commenting on the 2005 CNN article and the “No brain, no pain” meme, one Associate Professor of Biology who specializes in crustacean neurobiology at The University of Texas-Pan American wrote, “I won’t comment on the pain portion, but as to the claim that a lobster has no brain? It is wrong. It is false. It is incorrect. It is untrue. I don’t know how much more flatly I can say it. Lobsters have brains. So do crabs and crayfish and other crustaceans”

There have been numerous studies relevant to crustacean nociception, pain, and sentience but they have had mixed results, some of the positive studies made conclusions such as “We conclude that there is considerable similarity of function, although different systems are used, and thus there might be a similar experience in terms of suffering.“, “The results are consistent with the idea of pain in these animals.“, andThese findings are consistent with the idea of a pain experience rather than a nociceptive reflex.” A 2009 review of the published evidence lead one researcher to write

“A number of studies, although not specifically directed to the issue of pain, shows the ability of crustacean decapods to display such a rich behavioural repertoire that, if exhibited by vertebrates, would have been considered to be indicative of higher mental faculties. Again, the underlying rationale is that animals that possess such behaviours are sentient and may experience pain. Understandably, complexity in behaviour does not indicate consciousness but it may set out the basis for it”.

One  study published in Animal Behavior in 2008, showed that when acetic acid was applied to the antenna of prawns that they would groom the afflicted antenna and rub it on the side of the tank. Benzocaine, a local anesthetic, was found to inhibit this grooming and rubbing response without altering their general swimming activity. The researchers concluded, “The inhibition by a local anaesthetic is similar to observations on vertebrates and is consistent with the idea that these crustaceans can experience pain.”

On the other hand a similar study from 2010, looking at different species than the 2008 study, found “no change in behaviour… compared to controls“, concluding that,  “previously reported responses to extreme pH are either not consistently evoked across species or were mischaracterized as nociception. There was no behavioural or physiological evidence that the antennae contained specialized nociceptors that responded to pH.”  Unfortunately the nuance was lost on many and the author felt the need to clarify by pointing out on their blog a critical point from the paper, “we are not claiming that crustaceans do not have nociceptors. We are not claiming that crustaceans do not feel pain. Indeed, as we have emphasized, there are many reasons to expect that they could, making the results presented here all the more surprising.”

Similarly, experiments looking at changes in defensive behavior after administering injections of morphine and naloxone to crabs has yielded mixed results (1, 2, 3). Other evidence seems to demonstrates that crustaceans also may not be merely mindless automatons but rather posses some degree of agency, i.e. the ability to act outside of unconscious reaction & instinct. All that being said, pain is only one aspect of sentience and we should also be aware that different species cant develop widely different capacities and ways of interacting with the world. We also must be wary of being anthropocentric or vertebracentric (as some have called it) by only making direct comparisons to vertebrate physiology which are not always appropriate since nerves and brain regions can be co-opted for different purposes among different species.

So what does this all mean? We are left in the position of making an educated guess. We have to weigh the evidence and consider the potential ethical ramifications. Most of all we must learn to become comfortable with a degree of uncertainty. But even without perfect evidence we eventually need to make the decision of whether we will eat lobster and crab or not. To me, evidence of the possibility of some form of sentience in crustaceans and the potential costs of imposing suffering and ending an experience of life are just too great to ignore. I think Peter Singer had it right when he wrote,

“If crustacea can suffer, there must be a great deal of suffering involved, not only in the method by which they are killed, but also in the ways in which they are transported and kept alive at markets. To keep them fresh they are frequently simply packed, alive, on top of each other. So even if there is some room for doubt about the capacity of these animals to feel pain, the fact that they may be suffering a great deal, combined with the absence of any need to eat them on our part, makes the verdict plain: they should receive the benefit of the doubt.

Update 1/21/13: A new study titled, Shock avoidance by discrimination learning in the shore crab (Carcinus maenas) is consistent with a key criterion for pain adds another data point and concludes,

These data, and those of other recent experiments, are consistent with key criteria for pain experience and are broadly similar to those from vertebrate studies.

13 Responses to “Pain in Crustaceans?”

  1. kitchenmyths Says:

    I am the KitchenMyths guy – I didn’t know how else to contact you regarding your post on lobsters and pain. I am not going to approve your comment for two reasons. First, it is too long. Second, it is essentially a word-for-word copy and paste of material that is already on the web. This is not the purpose of comments in my blog, which are for personal responses and not to reproduce material that is elsewhere. Finally, it contains much information that is just plain wrong as well as logically untenable conclusions – I am a biologist of 40 years experience and I know what I’m talking about. If you want to submit a short comment with a link to this material elsewhere, that will be a different matter.

    • skepticalvegan Says:

      Actually I wrote that comment myself. Only ONE sentence (an extract from a relevant study) was copy and pasted. If you feel the rest is a word-for-word copy and paste or a “reproduction” please find the source material, should be easy with google. As for my comment or post being wrong, I tried to stick to the scientific evidence and arrived at an uncertain conclusion, your post just presented too much conjecture and no real evidence. I could not provide a adequately short comment critiquing your post as it is a complex issue, I could just say “you’re wrong, here look at this website” but I choose to do research myself and provide a “personal response”.
      Anyways, really, a comment too long to publish? I get far far longer critical comments here and still take the time to answer them. Also what is the cut off as far as word count? Because you have at least one comment that is 261 words while mine is only slightly longer at 278 words…

      And just so folks can see the comment we are referring to, this is about a comment I attempted to post on the Kitchen Myths blog post about lobster, I’ll re-post it here and let the readers judge

      skepticalvegan June 25, 2011 at 6:33 pm Your comment is awaiting moderation.

      “I welcome comments regardless of whether you agree with me. Profanity, personal attacks, and name-calling are not acceptable.”

      Then why will you not publish the following comment, which contains neither profanity, name-calling, or a personal attack but rather a hearty disagreement that cited plenty of scientific research. If you still feel it is rude then by all means edit out the rude part, but address the science please.

      “lobsters and other crustaceans are not vertebrates and simply do not have these nerve pathways and brain regions (they don’t have a real brain at all, for that matter). In other words, no brain, no pain”

      First, They do have a brain*…ask a biologist…or two (& this guy doesn’t even support the idea that lobster feel pain)
      or a simple diagram here
      *as well as nociceptors, opioid receptors, & prostaglandins

      Second, the research on nociception and pain in crustaceans (various species), while mixed and inconclusive at this point, still allows for a strong possibility that crustaceans feel pain. Indeed the evidence from behavioral observations, neurobiology, & experiments using pain inducing and pain killing substances actually seems to lean in favor of the pain hypothesis not the other way as you seem to conclude with the cave fish analogy, my guess is that you made the wrong guess. At the very least we seem to have no actual need for lobster flesh and enough evidence to give them the benefit of the doubt and leave them be.

      some papers…
      “The inhibition by a local anesthetic is similar to observations on vertebrates and is consistent with the idea that these crustaceans can experience pain.”

  2. Veganofilo Says:

    “I am a biologist of 40 years experience and I know what I’m talking about.”

    Argument from authority

  3. Anna Says:

    It’s strange that people sometimes carry over an older mindset to new technologies. Like when I got my digital camera, I was very careful about what I took pictures of, as if I had a roll of film and could only take 24 pictures! And then sometimes people don’t want to publish blog comments because they are “too long” — blogs aren’t newspapers or magazines, and the people who run them don’t have the same concerns over space that editors of paper-based media do …

  4. The Humane Hominid Says:

    “I am a biologist of 40 years experience blah blah blah…”

    Who cares? Address the argument or abstain from input.

  5. mikekoz68 Says:

    So,in conclusion, lobsters don’t feel pain? OK good.

    • skepticalvegan Says:

      Are you sure you read the full post and linked studies? The point was the evidence is mixed but there may be reason to give them the benefit of the doubt. It might be more valid for you to say “the evidence is not convincing at this point that lobsters feel pain” but it’s not conclusive by any means.

  6. A diary of an animal lover Says:

    I agree completely about giving them the benfit of the doubt. How can we not? Very interesting post.

    A rather infuriating reply from kitchenmyths, handled perfectly, I think this shows in his lack of further conversation.

  7. Anabela Pinto Says:

    Pain and suffering are two different concepts. Pain is difficult to be defined as we associate it with awareness of suffering. However in neurological terms, pain is information that causes a withdrawal behaviour and is detected by specialised neurons in animals that have neurons. Furthermore, if we want to go backwards in evolution, such nociceptors evolved from similar cellular structures. One could also say that amoebas and bacteria experience “pain” since they withdraw from noxious stimulus.
    Pain and suffering are two different issues. Suffering assumes the presence of a thing called “the mind” which is present in most vertebrates offering different levels of complexity.
    Do lobsters have a mind? Difficult to say. We know that chepalopods ( octopuses) have a great ability for learning. Dies it bring them the ability to suffer? The truth is that the species Octopus vulgaris is protected under the Animals Scientific Procedures Act in the UK, which regulates the use of animals in experiments.
    No scientist with a background in the life sciences would deny that all animals can feel noxious stimulus and withdraw from them. After all that is evolution.. if they didn’t they would have been extinct by now. The tricky question is why did animals have evolved the capacity for suffering, even when no physical pain is present? I mean with pain, the damage of tissues and structures.

  8. vigila Says:

    The whole point here is lost. Of course many organisms are equipped with the ability to avoid condition that can be harmful to that. Like Pinto (above) said. Non-humans did not evolve to analyse and think critically as well as the ability to form logical rational life choices so exceptionally great. Some people got it better honed.

    Even we have immediate reaction with no awareness. The last time you touched the hot stove you moved away immediately, so before you even register it you are saved from harm’s way. That is the sort of thing lobsters and many other organisms ‘feel’.

    Does it suffer, get angry, upset, feel really really worn old weary and tired? I say not. Survival and breeding(continuity of it’s OWN gene) is going to be the goal in it’s mind. They simply aren’t capable.

    It is nothing like humans and our close relatives.

    In conclusion, the more aware, conscientious and caring to others a being is I’d say the more evil it es to chop them up and do a stir-fry. That is of course, my personal opinion.

  9. Whitehead Says:

    Totally agree with the Peter Singer quote in your article. I came across the following article concerning hermit crabs, which seems to show that they can react to unpleasant stimuli.

    On a personal level, I find the thought of any creature being bolied alive disgusting, and watching that happening to a lobster is what started me away from meat in the first place.

  10. davidmikesimon Says:

    Do these data have any bearing on the possible status clams/mussels and similar creatures as being able to perceive pain?

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