The Case for Vegans Eating Oysters, Mussels, & Other Invertebrates?

Nope, Here’s Some Science.

If you’ve reached this article, then you are well acquainted with the definition of veganism, which is a stance against the purposeful exploitation of animal species as is practical. It’s troubling to find numerous members in the vegan community supporting the exploitation of animal species based on articles unsupported by a single shred of evidence. More alarming is how these articles try to establish oysters, mussels, and even other animals in the vegan community as being akin to plants, rocks, and as one stated, “a disembodied finger.”

Modern molecular and taxonomic advances have led scientists to base classification of living beings in very specific ways. I won’t further delve into the subject, but I will say that oysters and other animal species are not comparable to plants. The plant and animal kingdom are separate for good reason regardless of what supporters of bivalve eating in the vegan community will have you believe. One of the most important differences is that plants do not have a nervous system while bivalves do.

The same bivalve eating individuals claim that mussels and oysters are not sentient because they do not have “brains,” and while it is true that mussels and oyster do not have a brain in the sense that you or I do, they do have ganglia. Ganglia, in simple terms, is basically their form of a brain — how they get their systems to function and respond when they need to. Yes, invertebrates have much simpler nervous systems than vertebrates, but they still have nervous systems. How developed their nervous system depends on the species. More importantly, their form of a nervous system allows them to respond to their living conditions and survive in them.

Most, if not all, invertebrates have the capacity to detect and respond to noxious or aversive stimuli. That is, like vertebrates, they are capable of ‘nociception” (Smith 1991). Responses to negative stimuli, such as pain, which is very subjective depending on the individual, can indicate that something more than a simple nociceptive reflex is involved. Together, they may help the animal to recover from damage caused by the painful event and avoid being harmed in the future” (Smith 1991). While invertebrates probably do not feel pain in the same way humans do, Smith stated that, the issue isn’t closed. He further stated that, “Mather (1989) suggests, we should simply accept that these animals ‘are different from us, and wait for more data.’

It would be unreasonable to apply the same guidelines of pain that we apply to ourselves and other vertebrates to species that are completely different to us. Smith (1991) warned that, “pain might incorrectly be denied in certain invertebrates simply because they are so different from us and because we cannot imagine pain experienced in anything other than the vertebrate or, specifically, human sense.”

Unfortunately, “reports are notably lacking in sessile molluscs, primarily due to the difficulty of quantification of behaviours that occur in these generally small animals whose behaviour is characterized by minimal movement carried out over comparatively long time periods. Such movement may, however, be critical in survival and its quantification may provide insights into strategies and environmental conditions of consequence for this important animal group (Robson, Wilson, and Garcia de Leaniz 2007).”

Supporters of vegan bivalve eating claim mussels and oysters cannot respond to stimuli simply because their reaction to it doesn’t stem from a central nervous system while ignoring the fact that they do have a nervous system. However, if mussels and other bivalves are but barely living filtering rocks without the ability to respond to, well, anything, why do mussels, for example, have a need to detect and respond to predators, or even respond to stress at all?

As you may have noticed, I’ve taken most of my text from scientific literature. I am doing this on purpose to demonstrate that I am backing all my statements and thoughts on this subject with actual scientific evidence. To counter the misinformation being used to justify animal exploitation and to bring accurate science into the discussion, below, I attempt to set the science straight and provide examples that exemplify how those in support of eating these bivalves are erroneously advocating for unethical behavior in the vegan community. I also do not try to make the case (or not) for sentience because it just doesn’t make sense. You’ll see what I mean.


“Scientifically accepted definitions of pain and nociception neatly distinguish these concepts (e.g., Merskey and Bogduk 1994), but drawing a line between the two can be difficult in practice. Furthermore, no experimental observation of nonverbal animals (nonhumans) can demonstrate conclusively whether a subject experiences conscious pain (Allen 2004). Suggestive evidence for painlike experiences in some animals is available, and nociceptive responses measured at the neural and behavioral levels in molluscs have provided evidence that is both consistent and inconsistent with painlike states and functions. Unfortunately, inferences drawn from the relatively small body of relevant data in molluscs are limited and prone to anthropocentrism. Identifying signs of pain becomes increasingly difficult as the behavior and associated neural structures and physiology diverge from familiar mammalian patterns of behavior, physiology, and anatomy, making interpretation of responses in molluscs particularly difficult.” This does not only refer to cephalopods though. This is a general statement inclusive of all mollusks.

Gartner & Litvaikis (2013) found that blue mussels “selectively alter byssal thread production and movement in the presence of injured conspecifics and potential predators.” In addition, Robson, Wilson, and Garcia de Leaniz (2007) found that “mussel response to predation is graded and complex and may well indicate animal-based assessments of the trade-off between effective feeding and the likelihood of predation.” Couldn’t this be considered a form of decision-making?

Opioid receptors have also been observed and studied in mussels (Aiello 1986; Cadet and Stefano 1999) AND to quote the biggest proponent of bivalve eating in the vegan community, the Sentientist herself, “Many animals have opiate receptors, indicating they are making painkillers and regulating pain within their own nervous system.”

Well, “investigations have shown that similar opiate systems may have a functional role in invertebrate nociception (Fiorito, 1986; Kavaliers, 1988). In addition, “Opiate binding sites, with properties similar to those of mammalian opiate receptors, have been shown to be present in the neural tissue of the marine mollusk Mytilus edulis (Kavaliers et al., 1985).” It should be noted that M. edulis is a species of mussel.

In summary, studies that show the opposite of what the bivalve eating supports claim exist. Mussels have responses to stimuli (Stephano 2002), including stress (Anestis et al. 2008), and as we have seen, may make decisions based on threats of predation ((Gartner & Litvaikis (2013); Robson, Wilson, and Garcia de Leaniz (2007)).


Unlike plants, but like most other invertebrates, oysters do have nervous systems. How developed those systems are does not automatically reduce them to the level of plants. Because they have simple nervous systems does not mean that one can deduce that they are unable to respond to stimuli or have the inability to experience their own environment, particularly because we are incapable of truly understanding what pain and sentience are in other animals. 
 Carroll & Catapane (2007) stated that, “Bivalve molluscs [this includes oysters] have a relatively simple bilaterally symmetrical nervous system composed of paired cerebral, visceral and pedal ganglia, and several pairs of nerves. The cerebral ganglia (CG) are connected to the visceral ganglia (VG) by a paired cerebrovisceral connective and the VG innervate each gill via branchial nerves.”
 Unfortunately, based on my review of the available data, there aren’t that many studies focused on oysters. And those that exist seem to have an interest in human application or farming. As of this date, I could not find a specific paper devoted to the examination of nociception in oysters per se. However, that is not conclusive proof that nociception does not exist in oysters. 
 Here’s why:
 “The full length cDNA of a homologue of δ-opioid receptor (DOR) for [Met(5)]-enkaphalin was cloned from oyster Crassostrea gigas” by Liu et al (2015). These results, as outlined by Liu et al. (2015), “collectively suggested that CgDOR for [Met(5)]-enkephalin could modulate the haemocyte phagocytic and antibacterial functions through the second messengers Ca(2+) and cAMP, which might be requisite for pathogen elimination and homeostasis maintenance in oyster.” Varga et al. (2004) describe, “delta opioid receptor (DOR) agonists are attractive potential analgesics, since these compounds exhibit strong antinociceptive activity…”
In addition, mu opioid receptors have been found in both blue mussels (Mantione et al. 2010) and oysters (Zhang 2012); these receptors are also antinociceptors. 
Opioid peptides have also been documented in oysters. Liu, Chen, & Xu’s (2008) described that, “The nervous and immune systems of invertebrates can exchange information through neuropeptides. Furthermore, some opioid peptides can function as endogenous immune system messengers and participate in the regulation of the immune responses.” Their study concluded that their “data strongly suggests an involvement of opioid peptides in the regulation of the antioxidant defence systems of the Pacific Oyster.” Endogenous opioid peptides have been described as inducing, “analgesia in humans and antinociception in animals. These peptides act in several regions of the CNS to mediate pain control, because antinociception is observed in animals whether endogenous opioid peptides are administered into the peripheral circulation; into spinal sites; or into various regions of the brain, such as the raphe nuclei, PAG region, or medial preoptic area. Many events or stimuli that are experienced as painful, stressful, or traumatic can induce the release of endogenous opioid peptides. These peptides then act to make humans and animals less sensitive to noxious events by inducing euphoria and analgesia or antinociception(Froehlich 1997).” 
 Why would oyters have any of these receptors or mechanism for antinociceptive activity? If they have antinociceptors, does that mean that they could have noticeptors as well? Regardless, it has been established above that opioid receptors have been found in oysters, and “opiate systems may have a functional role in invertebrate nociception” (Fiorito, 1986; Kavaliers, 1988).
The following studies further show that oysters, although thought of as simplistic as plants by many, have nervous systems that are still complex and may use many of the same responses and regulations as other animal species.
Harrison et al. (2008) found that their study confirmed and quantified, “histamine as an endogenous biogenic amine in C. virginica in the nervous system and innervated organs…Histamine is a biogenic amine found in a wide variety of invertebrates, where it has been found to be involved in local immune responses as well as regulating physiological function in the gut. It also functions as a neurotransmitter, especially for sensory systems1. Histamine has been well studied in arthropods and gastropods, but has been rarely reported to be present or have a function in bivalves other than the limited reports identifying it in ganglia and nerve fibers of the Baltic clam.” The authors further stated that, “Bivalves, including the oyster, Crassostrea virginica, contain dopamine, serotonin and other biogenic amines in their nervous system and peripheral tissues. These biogenic amines serve as neurotransmitters and neurohormones and are important in the physiological functioning of the animal.” They also stated that,”The mantle rim of bivalves is a sensory structure containing various sensory receptors. The involvement of histamine in sensory systems of invertebrates, particularly gastropods, coupled with our preliminary physiology research, strongly suggest histamine to be a sensory neurotransmitter in the mantle rim of C. virginica.”
 In addition, Park et al. (2007) were able to clone and characterize, “Lipopolysaccharide-induced TNF-alpha factor (LITAF) is an important transcription factor that mediates the expression of inflammatory cytokines” in the Pacific oyster Crassostrea gigas.” Interestingly, Zhang & An (2007) describe that, “there is significant evidence showing that certain cytokines/chemokines are involved in not only the initiation but also the persistence of pathologic pain by directly activating nociceptive sensory neurons.
 Like in mussels, it has been shown that oysters control the beating of their cilia to draw in water, which they do as filter-feeders. Carroll & Catapane’s (2007) study demonstrated that there is a “reciprocal serotonergic-dopaminergic innervation of the lateral ciliated cells, similar to that of M. edulis, originating in the cerebral and visceral ganglia of the animal…” This, therefore, means that ganglia (their nervous system) regulates movement/behavior. Perhaps, like in mussels, oysters also have the ability to actively control, based on a form of decision-making, why they employ the types of ciliary movements they do.
 Regarding predation, “Bivalves readily utilize chemical exudates that emanate from predators and from injured conspecifics to evaluate predation risk (Caro & Castilla 2004, Cheung et al. 2004, Smee & Weissburg 2006b) (Robinson et al. (2014). A study by Robinson et al. (2014) found that in the presence of predators, “oysters grew shells that required more force to crush and resultantly were afforded greater protection from crab predators.” This supports recent studies that “have shown that oysters react to gastropod and crustacean predators by producing thicker, heavier shells (Newell et al. 2007, Johnson & Smee 2012, Lord & Whitlatch 2012)”(Robinson 2014). Again, these are examples that oysters actively respond to their environment (predation in this case) as any other animal species would when threatened. 
 The studies that I’ve quoted above are only bits and pieces of a large body of data that is yet to be uncovered or even studied. What all this means when put together is yet unknown because few studies have been done. However, it shows that although oysters have simple, yet efficient nervous system to respond to the type of lifestyle that they live, they also have sensory structures and receptors like those found in other animal species. In essence, they are still nothing like plants regardless if they are sessile species. The fact that they are sessile still does not mean that they do not need to react to their environment if simply to protect themselves and carry out functions in order to survive.

Sea Urchins

The same supporters of mussel and oyster eating have begun to further open their menus to other animal species not categorized as bivalves because of similar reasoning. One such supporter claims that because they don’t have eyes or a brain like vertebrates, they must be fair game to the vegan community.

When it comes to sea urchins, no they do not have eyes in the sense that we and other animals have eyes, but “it looks like the entire surface of their bodies are acting as one big eye…” said researcher Sönke Johnsen, a marine biologist at Duke University.” Johnsen is further quoted by the same article saying, “We think of animals that have a head with centralized nervous systems and all their sense organs on top as being the ones capable of sophisticated behavior, but we’re finding more and more some animals can do pretty complex behaviors using a completely different style.” (Choi 2009)
Blevins & Johnsen (2010) stated that their research study is the “first demonstration of spatial vision in an echinoderm sheds further light on the complex optical structures and photobehaviors found in this phylum.”
 “It appears that sea urchins may use the whole surface of their bodies as a compound eye, and the animals’ spines may shield their bodies from light coming from wide angles to enable them to pick out relatively fine visual detail….Some of the animals may interpret the object as a predator and flee, while others identify it as shelter and head towards it. What is more surprising is that the urchins’ vision is as good as Nautilus and horseshoe crab vision, which is quite impressive for an echinoid that has turned its whole body into an eye.”
(Knight 2010) 
 And on the claim that they “do not have centralized nervous systems” as basis to decide it’s ok to eat them, the fact remains that sea urchins and all echinoderms, including sea urchins, have nervous systems:
 Johnsen stated that, “Although sea urchins don’t have brains, “it could be their entire nervous system more or less acts as a brain,” Johnsen said. “In our case, we vertebrates have nervous systems that are more or less controlled by a central brain, but sea urchins have a pretty diffuse nerve net, where no region looks like a central processing unit as far as we can tell.” (Choi 2009)
 “The adult echinoid nervous system is comprised of 5 radial nerve cords, which are joined at their base by commissures that form a ring surrounding the mouth (Cobb, 1970; Cavey and Markel, 1994)… Tube feet, spines and pedicellariae have ganglia and a complement of sensory and motor neurons…The arrangement of the nervous system in echinoderms is a feature that distinguishes them from other deuterostomes (chordates and hemichordates). Echinoderm nervous systems are dispersed, but they are not a simple nerve net. The adult is not cephalized, yet the radial nerves are segmentally organized (Burke et al 2006).”
 Most importantly, Johnsen also states that, “We think of animals that have a head with centralized nervous systems and all their sense organs on top as being the ones capable of sophisticated behavior, but we’re finding more and more some animals can do pretty complex behaviors using a completely different style…In the beginning, people built robots like they would humans, with powerful central processing units, complex sensors and fairly complex rules for doing things…Now they’re finding it might be a lot better with a distributed system with many little processors and simpler sensors and simple rules, which end up creating fairly complicated behaviors as emergent properties, just as how a flock of birds can make intricate patterns without any one bird choosing these patterns.” (Choi 2009)
 Thus, not having a nervous system with a brain does not mean you are a living plant-like rock creature incapable of experiencing the world. Plants don’t have nervous systems. Echinoderms (and Bivalves) do have nervous systems regardless of how simple one believes them to be.

Pain in Invertebrates
 It is important to note that, “the clear distinction that once existed between the terms “pain” and “nociception” has become blurred recently, to the point that many neuroscientists and clinicians no longer make a distinction; that is, most accept that nociception is equivalent to pain.” (Sladky 2014)
 In his essay examining pain and analgesia in fish and invertebrates, Dr. Sladky, from the University of Wisconsin, asks, “can we recognise pain in fish and invertebrates? Is the perception of pain by a fish or an invertebrate equivalent to that of a mammal? We will never be able to fully and objectively answer these questions, because the animals simply cannot tell us…Could it be that recognition of pain in fish and invertebrates is impeded by our inability to empathise with species that do not convey distress through facial expressions, do not vocalise in response to distress, and are not warm and fuzzy?”
 Dr. Sladky states that “our limited understanding of pain and analgesia in fish and invertebrates should not obscure our clinical decisions, and we should err on the side of fish and invertebrate well-being by making the assumption that conditions considered painful in humans and other mammals should be assumed to be potentially painful across all other vertebrate and invertebrate species.”
 “Although peripheral nociceptors have not been identified in cephalopods, there are no published reports that anyone has investigated peripheral nociception in cephalopods. On the other hand, nociceptors have been identified in anemones, sea cucumbers, leeches, nematodes, Drosophila, and many other insects (Kavaliers 1988; Tobin & Bargmann 2004; Xu, et al. 2006; Smith & Lewin 2009; Puri & Faulkes 2010)…Many invertebrate species (earthworms, roundworms, molluscs, Drosophila) possess endogenous opioid receptors (Dalton & Widdowson 1989; Tobin & Bargmann 2004). Immunohistochemical staining indicated the presence of endogenous opioid receptors in nematodes (Prior et al. 2007). Mussels possess benzodiazepine and opioid receptors in their nervous systems (Gagne et al. 2010). In addition, there is genetic and physiologic evidence that invertebrates and vertebrates may have similar capacities with respect to pain and analgesia…”(Sladky 2014)
 “Pain-associated behaviour of invertebrates has been described in multiple species. In sea anemones, crabs, crayfish, sea slugs, snails, flatworms, crickets, praying mantis and Drosophila, withdrawal responses are observed with thermal and mechanical noxious stimuli…”(Sladky 2014). 
 The paper by Dr. Sladky is definitely worth the read because it is a nice summary of all the discoveries that have been made about fish and invertebrates with relation to pain. Read it here:
 In essense…
 Albeit slowly, science has shown us that invertebrate species are not as simple as we once thought. So I ask, what basis is there for not erring on the side that potentially oysters, and other invertebrates, that have yet to be studied in detail, also have the ability for these mechanisms and behaviors?

Would it not be unethical to apply standards to species that science has yet to fully study or understand?

Would it not be unethical and unfair to apply specific standards to species with completely different body forms that work in completely different ways than we could ever imagine?