Multiple people have insisted to me that “peer-reviewed science” had “proven” that shrimp suffer and thus deserve our focus.
Below is Rob Velzeboer’s research report (with ChatGPT, reviewed by me and Anne) regarding what actual evidence we have regarding shrimp. Rob focused on the morally-relevant issue of subjective experience, not just the ability to “sense.”
I will add one thing to the Conclusion: The recent EA charity collection featured multiple organizations focused on shrimp and arthropods. Only one – Legal Impact for Chickens – focuses on factory-farmed chickens. In just a few months, advocacy for shrimp raised more money than chicken advocacy organization One Step for Animals has received in 11+ years; One Step will probably cease to exist in a few years due to a lack of funding.
Over the years, various people have asked me why I harp on suffering versus math / expected value so much. It is because each one of us has the ability to help many individuals who are horribly and unnecessarily suffering (e.g., examples that came in while I was working on this introduction: 1, 2). Yet, the “hip” thing is to focus attention and millions of dollars on “mathy” areas, such as creatures who probably don’t suffer at all; even if they do, their maximum suffering is negligible compared to others we could help.
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Do the Shrimp We Eat Actually Suffer?
Scientific and public interest in animal sentience has expanded rapidly, especially for animals outside the usual vertebrate focus. Decapod crustaceans – crabs, lobsters, prawns, and shrimp – have become a central case study. This recent attention has been shaped by a handful of major reviews, including a comprehensive PeerJ synthesis and the London School of Economics (LSE) “Decapod Sentience” report. These reviews evaluate the scattered literature and help determine which animals might genuinely have the subjective, conscious experience of suffering.
Across these assessments, a consistent pattern emerges. Some decapods, such as crabs and lobsters, show reasonably strong evidence for pain-like experience. But for the shrimp humans eat most commonly – Litopenaeus vannamei and Penaeus monodon – the evidence is thin, fragmented, contradictory, and highly uncertain.
Minimal but Plausible Foundations: What We Know About Nociception
Before scientists can talk about suffering and pain, they look for the most basic requirement: nociception, the ability to detect harmful or irritating stimuli. Here the evidence for penaeid shrimp – those we eat – is reasonably solid. Both the PeerJ review and the LSE report give them “High” confidence for nociceptors, meaning they have sensory neurons tuned to potentially damaging events.
But nociception is not pain, let alone suffering. A reaction to a harmful stimulus does not, by itself, imply any subjective experience. For there to be evidence of possible conscious experience of pain, signs of deeper processing, such as learning from harm or weighing avoidance against competing needs are required. [This is necessary but not sufficient, though, given our lack of understanding of consciousness. It is easy to imagine robots able to react to harmful stimuli and learn from “pain” without any subjective suffering. -ed]
Only one line of evidence in the shrimp species we farm the most, L. vannamei, indicates even the start of this process. During eyestalk ablation, L. vannamei show escape behaviours: erratic swimming, tail flicks, and attempts to withdraw. Applying lidocaine has been shown to reduce these reactions.
On the surface, this might suggest that something is being suppressed. But lidocaine introduces a major interpretive problem: anaesthetics can reduce movement simply because they sedate the animal, not because they relieve any subjective experience of pain. A sedated shrimp might move less regardless of how it “feels.”
More importantly, blocking the signalling of neurons with lidocaine would reduce even reflexive, non-conscious harm-avoidance, like disabling a sensor on a robot. With no follow-up, the finding remains highly ambiguous.
Behavioural Ambiguities: Rubbing, Grooming, and Failed Replications
Researchers have also looked to behaviours that seem more complex than reflex withdrawal – particularly targeted grooming or rubbing of a body part after irritation. One early study on Palaemon elegans, a shrimp-like crustacean, found that applying acetic acid or sodium hydroxide to a single antenna led to sustained, location-specific grooming, and that these behaviours were reduced by local anaesthetic.
This initially appeared to be a potential indicator of pain-like reaction. But a later replication attempt by Puri and Faulkes (2010) tested the same idea in three species:
Litopenaeus setiferus (a close relative of L. vannamei),
Procambarus clarkii (red swamp crayfish), and
Macrobrachium rosenbergii (giant freshwater prawn).
All three are decapods, but importantly: two are actual shrimps/prawns, and one is a crayfish, so these were not distant comparisons.
Across all species tested, the authors found:
No directed grooming or rubbing in response to the same kinds of chemical irritants.
No behavioural reaction even when stronger stimuli were used.
No evidence of pH-sensitive nociceptors in the antennae.
These results directly contradict the earlier claims regarding P. elegans. They also illustrate how fragile the evidence base is: one shrimp-like species is reported to have shown a behaviour interpreted as pain-like, while closely related species – including one nearly identical to the shrimp we farm – show nothing. Sceptical reviewers (e.g., Key et al. 2022) point to these failures of replication as major reasons to doubt strong claims of pain in shrimp.
Evaluating the Criteria: Where Penaeid Shrimp Score Low
Modern sentience frameworks assess evidence across multiple dimensions:
Possession of nociceptors (i.e., receptors tuned to noxious stimuli)
Possession of integrative brain regions (brain structures capable of integrating sensory and other information)
Connections between nociceptors and integrative brain regions (i.e., plausible neural pathways from detection to central processing)
Modulation of responses by analgesics, anaesthetics, or opioids (i.e., evidence that application of such substances reduces reactions to noxious stimuli)
Motivational trade-offs (behaviour indicating that the animal trades off potential harm against reward or other needs)
Flexible self-protection behaviours (for example, wound-directed grooming, guarding, protective postures)
Associative learning (especially avoidance learning) – learning to avoid stimuli previously associated with harm.
Behavioural indicators of negative affective states (broadly: behaviour plausibly consistent with distress, rather than mere reflex withdrawal)
Penaeid shrimp score:
High for nociceptors
Medium (at best) for modulation of responses (based on one non-replicated lidocaine study)
Low or Very Low for all other criteria
Importantly, these low ratings are not “proof of absence.” They reflect how little research has been done and how few studies test for complex behaviours. The PeerJ review notes that “negative affective states remain undetermined,” meaning that we simply lack the kind of evidence that would allow a remotely confident inclination either way.
The Big Missing Piece: Decision-Making and Motivation
The strongest evidence for pain in crabs and lobsters comes from studies showing:
learned avoidance of harmful stimuli,
balancing avoidance against food, shelter, or mating opportunities,
persistent protective behaviour long after injury,
and flexible responses that change with context.
These are not immediate reflexes – they indicate some further evaluation, which could be suggestive of (but not proof of) subjective experience.
For penaeid shrimp, none of these behaviours have been demonstrated. There is currently no evidence that they learn from injury, make trade-offs, or alter behaviour in a long-term, sustained, adaptive way. Without decision-level evidence, claims of pain (let alone suffering) remain speculative at best.
Policy, Precaution, and Divergent Interpretations
The UK government now classifies all decapods, including shrimp, as sentient animals. But the LSE authors explicitly state that the inclusion of shrimp rests on precaution and on evidence from better-studied decapods – not on strong data specific to L. vannamei or P. monodon.
Sceptics argue that, without robust evidence, interpreting shrimp reactions as the subjective experience of pain risks mistaking simple reflex arcs or sedation effects for conscious, morally-relevant experience, especially given conflicting evidence on self-protective behaviours (wound grooming).
Bottom Line: Real Uncertainty, Minimal Evidence, and a Broader Ethical Context
At present, the scientific record provides some weak (and contradicting) evidence that the shrimp we eat might have some minimal capacity for sensing adverse stimuli. They have nociceptors. One study that failed replication indicated one shrimp-like species reacts to injury.
But the deeper hallmarks of subjective, experienced pain – learning, motivation, decision-making, context-sensitivity – have not been shown. The most widely farmed species, L. vannamei, has only one indirect study on a highly artificial procedure. P. monodon has no direct evidence at all.
Thus the most honest assessment is this:
Shrimp may or may not feel pain, and we do not yet know whether any such experience would be meaningful or morally weighty. The actual evidence does not meet the criteria for or support any claim of suffering. The question is profoundly understudied.
Conclusion: the broader, more important point
While shrimp remain an open scientific question, other forms of industrial animal production – particularly broiler chicken farming and the intensive confinement of pigs – are not uncertain in the slightest. For chickens, the evidence of severe and prolonged suffering is overwhelming. Lameness, bone deformities, chronic pain, rapid-growth pathologies, heat stress, and overcrowding are documented across thousands of studies. Their long-term behavior meets all the criteria that scientists have associated with suffering. The suffering is intense and the scale is immense. Unlike shrimp, the existence of deep, meaningful, subjective pain in chickens is not a scientific mystery.
So while shrimp deserve better research, they should not distract from the places where we already know, with absolute clarity, that animals experience intense suffering at industrial scale – especially those individuals, such as chickens, who receive relatively minimal attention.
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