Do Fish and Shrimp Suffer Agonizing Pain and Excruciating Deaths?

Philosophers and activists argue that fish and shrimp experience enormous amounts of agonizing pain, but the science behind their claims is far from convincing.

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This is not a specifically feminist piece, although it does touch on issues also related to feminist theorizing, such as cancel culture. As a tropical fish enthusiast, I am fascinated by the current debate on fish and shrimp consciousness, and I want to present an analysis as to why I am skeptical of much of the current discourse, as well as many charities that have collected thousands of dollars to supposedly end or relieve shrimp suffering.

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In the last few months, it’s become popular for philosophers and animal rights activists on Substack to promote veganism and to donate to charities that purport to end pain in invertebrates, especially shrimp. Prominent Substack writers have donated thousands of dollars to these charities, and it appears there is a widespread belief that the science is largely settled in the direction of fish and shrimp experiencing agonizing pain. Some Substack writers go farther, musing that these animals experience so much suffering it may be better that their species go extinct than allow them to suffer in the wild.

While there are several assumptions here that could be challenged, I want to focus in this piece on the assertion that science has proven that fish and shrimp, as well as “lesser” invertebrates like insects, feel agonizing pain comparable to the sorts humans feel. I argue that we have much more reason to doubt this assertion than to believe it. The arguments used by these activists - that fish and shrimp have pain receptors and that fish and shrimp demonstrate behaviors that prove pain experience - are backed by weak research that often failed to replicate and further fails to prove what it aims to show. Worse, there is evidence that uncritically accepting these arguments and the social policies these activists propose could have disastrous environmental consequences.

Before I proceed, I want to note that there is a default belief among many well-meaning environmentalists that empathy for animals requires assuming that their experience of the world is roughly similar to our own. This is an understandable position, but I think we should also be clear that a desire to show empathy for animals should not lead anyone to endorse bad science if the facts suggest that animals like shrimp and fish do not experience pain the way we do. Nor should we malign scientists as cruel or uncaring if those scientists make good faith arguments to show that it is unlikely to be the case that these animals feel pain.

Unfortunately, as with many controversial topics where activism intersects with science and philosophy, ad hominem and cancel culture attacks have flourished against scientists who take a more skeptical position, regardless of the strength of their arguments. This culture of shaming and attacking those skeptical of fish and invertebrate pain should lead us to be skeptical of claims that the debate is completely settled in the pro-pain direction:

When the evidence for fish and invertebrate pain was found wanting, some of the researchers who conclude that fish are sentient and feel pain attempted to direct attention away from the evidence that contradicted their assertions by discrediting skeptical scientists and labeling them “deniers”, “creationists”, or even “racists”. Demeaning and factually incorrect attacks in pseudo-journals, online, or in the popular media are cleverly potent, because they are often repeated unquestioningly by those unfamiliar with the underlying science, particularly in social media forums, special interest groups and the press.

Unfortunately, such activities also lead to completely unacceptable outcomes, including attempts at public shaming by activist groups, and even anonymous threats of violence and intimidation which create a climate of fear amongst skeptics, who understandably wish to avoid such constant attacks.

Diggles et al, Reasons to Be Skeptical about Sentience and Pain in Fishes and Aquatic Invertebrates

The Case Against Fish (and Invertebrate) Pain

The case against fish and invertebrate pain is pretty simple. I will paraphrase the argument given by Brian Key and other neuroscientists here:

1. Pain is a product of the brain.

2. In particular, for pain to exist in an organism, the brain of the organism must sustain the sorts of neurological features that allow for consciousness and pain perception. In humans, this is the cortex, which performs the signal amplification and integration necessary for any particular nerve firing to be felt as pain.

3. Fish and invertebrates lack those neurological structures that can perform those tasks. They lack a cortex, and no “substitute” part of the fish or invertebrate brain can perform the task of signal amplification or integration necessary for the firing of a nerve to be felt as pain.

4. Therefore, fish do not feel pain, and neither do animals that similarly lack those neural structures.

It is critical to clarify that Key’s argument is not that specifically human brain structures are necessary for pain perception to exist. As Key repeatedly points out, this is a strawman of his position. Nor is it that these animals simply lack “enough” neurons to feel pain. Rather, it is that any animal that experiences human-typical pain must have some neurological structure that performs the functions necessary for human-typical pain. (While fish are the target of Key’s original paper, his arguments also apply to any invertebrate species that has similar or less complex brain structures, including shrimp.)

Conscious processing [of pain] is dependent on at least two non-mutually exclusive processes: signal amplification and global integration... Amplification provides a mechanism to increase signal-to-noise ratio and to produce ongoing neural activity after the initial sensory stimulus has ceased (Murphy and Miller, 2009). Global integration ensures the propagation and sharing of neural information so that the most appropriate response is generated in the context of current and past experiences.

Brian Key, Why Fish Do Not Feel Pain

Fish brains are pretty simple, and no part of the fish brain seems a good candidate for sustaining conscious pain perception.

Brian Key also anticipates the objection that fish do not feel “human pain”, but instead feel “fish pain”, which supposedly does not require a cortex. Key points out that such pain would still require conscious processing, and that such conscious processing would still require the features described above.

The proposition that fish feel “fish pain” (or pain by any other name, such as “raw experience” or “primitive feelings”) is not an argument for fish feeling with another part of their brain. If “fish pain” existed, it would need to be consciously processed using at least the minimal neural architecture described above. Thus, in the absence of this architecture, fish cannot feel any sort of pain. Fish clearly respond to noxious stimuli, and they do so by using feedforward circuitry to execute motor programs.

Brian Key, Why Fish Do Not Feel Pain

Counterarguments

Other parts of the fish/invertebrate brain sustain conscious pain perception

Some scientists have suggested that the fish brain stem or the optic tectum can sustain conscious perception of fish pain. Merker suggests, from a study of anencephalic children, that the brain stem can support conscious experiences. Key has responded by pointing out that those anencephalic children who seem to have basic conscious experiences likely simply have some remnants of a cortex which can sustain some conscious experience. The vast majority of anencephalic children are vegetative and moribund; if the brain stem were capable of sustaining conscious experience, we would expect all of them to show similar levels of consciousness, given that all of them still have intact and fully functional brain stems. But the lack of conscious awareness in the vast majority of anencephalic children suggests that the brain stem on its own is simply not capable of sustaining consciousness.

Other scientists, such as Michael Woodruff, have suggested that the optic region sustains consciousness in fish. But Key points out that ablation of this region doesn’t affect fish responses to touch or electric shock and is uninvolved in nociception. Therefore, this region also can’t be what supports conscious experience in fish. There simply do not appear to be other good candidates for sustaining conscious experience in fish or other invertebrates like shrimp, and the most straightforward conclusion is that fish do not feel pain; neither do other animals with similar or lesser brain structures.

Fish/Invertebrate Behavior Proves They Experience Pain

By far the most popular argument for fish/invertebrate pain is that these organisms demonstrate complex behaviors and act as if they are experiencing pain. Various philosophers have cited studies that they claim prove fish and other invertebrates feel pain, such as Sneddon’s “lip injection” study, in which scientist Lynne Sneddon injected acid into fish lips and claimed they demonstrated behaviors (rocking and rubbing) that proved they were experiencing pain.

These studies suffer from two problems. One, critics of Sneddon et al have pointed out that this study and other commonly cited studies fail to replicate. For instance, key results in this study (which was cited in the article “Betting on Ubiquitous Pain” by Bentham’s Bulldog as well as “The Case for Dumping Money into the Ocean” by Glenn), in which trout supposedly reacted to acid injected into their lips, failed to replicate. (An extended examination of the replication crisis in fish/shrimp pain studies can be found here.) A major study used to claim shrimp feel pain from acid was invalidated when it was discovered shrimp lacked nociceptors that detected acids or bases; in fact, the study’s authors had likely simply mistaken normal grooming behaviors as pain behaviors. Yet the results of these studies continue to be disseminated by pro-pain researchers and activists despite their lack of replication.

The second, larger issue with this argument is that it falsely assumes that complex behaviors indicate consciousness and that conscious pain perception must have deep evolutionary origins. As Paul Hart elegantly points out, however, even much human behavior can be performed unconsciously, and there is no reason to assume that complex behaviors performed by fish and shrimp must also be conscious:

For most humans, the myth of conscious control of their lives is so powerful and persuasive that action without it, even in non-humans, seems impossible. If, instead, one takes the view that many of the complex behaviors that we employ are monitored and informed by consciousness but are not directed by it, then we are freer to assess non-human behavior for what it is. If humans can drive a car, walk, give birth to a baby, play the violin, produce sentences in speech, all without the aid of conscious direction then surely non-human animals can also do complex things without conscious direction.

Paul Hart, Exploring the limits to our understanding of whether fish feel pain

Finally, critics of the pro-pain side point out that pro-pain researchers ignore animal behaviors that appear to starkly conflict with the idea that such animals experience human-typical “agonizing pain.” For example, crustaceans like shrimp are known to engage in autophagy, or eating their own body parts. This behavior is bizarre if it is assumed they feel human-typical agonizing pains.

Fish have C-Fibers, so they must experience agonizing pain

C-fiber nociceptors are responsible for agonizing pain in humans. The discovery of c-fibers in teleost (but not elasmobranch) fish was used by pro-fish-pain researchers as evidence of fish pain, but critics pointed out that the number of c-fibers in teleost fish was too low to sustain pain perception. That’s because humans become insensitive to pain when they are born with a congenital disorder that results in low levels of C-fibers (which are nevertheless higher than the levels found in fish!) It seems far more likely that these nociceptors play some other role in fish biology.

Ironically, contra the fish pain proponents, a fuller examination of C-fibers in fish and comparison to humans leads to the conclusion that they likely do not suffer the sorts of agonizing pains Bentham and others claim that they do:

It appears most logical to assume that in teleosts, at least those species that have been studied, A-delta afferents serve to signal potentially injurious events rapidly, thereby triggering escape and avoidance responses, but that the paucity of C fibers that mediate slow, agonizing, second pain and pathological pain states (in organisms capable of consciousness) is not a functional domain of nociception in fishes.

Diggles et al, Reasons to Be Skeptical about Sentience and Pain in Fishes and Aquatic Invertebrates

It is worth noting that shrimp have not been found to have these nociceptors at all. This makes the claim that shrimp experience X percent of the agonizing pain that a human feels suspect. This calls into question the efficacy of charities which have collected thousands of dollars to give shrimp “painless” deaths.

The Risks of Accepting the Pro-Pain Position

Severe Environmental Impacts

Pro-pain researchers sometimes present their work as having few risks. The idea is that the policies favored by pro-pain researchers have no environmental or other downsides; even if you are skeptical of their conclusions, you should accept their reasoning and their policy proposals to be on the “safe side”.

In fact, ecologists have pointed out that some of the policies favored by pro-pain researchers could have massive detrimental environmental impacts. An example is elaborated below; the demand to end eyestalk ablation on shrimp due to risk of shrimp pain could cause severe environmental and economic impact.

Demands by certain interest groups to ban eyestalk ablation in all shrimp farming would result in the use of ten to twenty times more P. monodon broodstock to meet industry needs for post larvae. This would immediately have the unintended consequence of requiring many more P. monodon broodstock, another “lose-lose” situation as it conflicts with one of the basic 3Rs welfare principles of reduction of numbers of animals used. Such a move would also increase fishing pressure on wild stocks, while the lack of reliable larval supply would threaten entire aquaculture industries in countries where P. vannamei is not available, threatening livelihoods and regional and/or global food security.

Diggles et al, Reasons to Be Skeptical about Sentience and Pain in Fishes and Aquatic Invertebrates

Philosophical Inconsistency Leading to Speciesism

Critics of fish pain research have pointed out that pro-pain philosophers apply their criteria for sentience and pain perception arbitrarily. For example, even slime molds are alleged to show behavior based evidence of sentience that should make them candidates for protection from “pain.” Yet pro-pain researchers don’t suggest environmental protections should be extended to these organisms.

…Slime molds are alleged to exhibit learning and problem-solving behaviors… Indeed, such behavior is not restricted to microorganisms from the animal kingdom, given that plants make sounds when stressed by dehydration.

Essentially, all of this means that if the criteria used by Birch et al. were universally applied, there is a high chance that few, if any, organisms would fail to meet their threshold for “some evidence of sentience”. Such an outcome brings the utility and validity of the criteria themselves into serious question.

Diggles et al, Reasons to Be Skeptical about Sentience and Pain in Fishes and Aquatic Invertebrates

When pressed, “pro-pain” researchers have denied that such organisms experience pain because they lack the neurological structures necessary for conscious perception, regardless of whether their behaviors would place them in the “likely sentient” category. Ironically, this is the exact reasoning used by the fish pain skeptics like Key! If an animal lacks the neurological grounding to experience conscious pain perception, it should not be assumed to experience pain regardless of its outward behaviors. The inconsistent application of this logic suggests that pro-pain researchers may themselves be subject to the speciesism they decry in others.

Conclusion

Various activists have claimed that fish and shrimp suffer in such agonizing ways that it might be better if we sought ways to end their existence entirely. They have further successfully encouraged various internet personalities to donate thousands of dollars to organizations intended to end shrimp or fish suffering. Such activists and philosophers typically present the idea that shrimp and fish suffer in agonizing ways akin to how humans might suffer as settled science:

Finally, the most detailed report ever compiled on the subject of animal sentience concluded that animals feel fairly intense pain. Shrimp, for instance, were estimated to feel pain, on average, 19% as intensely as we do.

Bentham’s Bulldog, Betting on Ubiquitous Pain,

Contra these activists and philosophers, I argue that the debate is far from settled, and that a fair examination of the counter arguments strongly suggests we should believe fish and shrimp do not experience untold amounts of human-like suffering; further, we can’t and shouldn’t estimate that shrimp or similar animals suffer some arbitrary percent “as much” as humans.

Finally, I believe this is great news for anyone who cares about the welfare of these animals. If Brian Key and similar authors are right, the world is full of far less suffering than Bentham, Glenn, and others suggest. There is no reason for us to consider that genetically engineering fish or invertebrate populations to avoid pain perception might be morally obligatory. And we can dismiss more fanciful arguments that we should seek to end the existence of those species entirely.