I love a good debate about what counts as “vegan” and what doesn’t… So let’s talk about oysters and other bivalves. They are animals, and vegans don’t eat animals—right? But a certain group of vegans, called ostrovegans, actually do eat bivalves.
What is an ostrovegan? An ostrovegan is a vegan who eats bivalves (oysters, mussels, and potentially clams and scallops). Ostrovegans, also known as bivalvegans, consider it morally acceptable and nutritionally beneficial to eat bivalves because these animals don’t have a central nervous system and likely do not feel pain.
This issue of whether vegans should eat bivalves is actually very controversial. It strikes to the core of what it means to be vegan because bivalves are animals, but they are likely not sentient animals (although that, too, is debated). Read along, and I’ll explain it all!
Definition of Ostrovegan and Bivalvegan
The most common definition of “vegan” is someone who doesn’t eat or use animal products—usually for ethical and/or nutritional reasons. The prefix “ostro” in ostrovegan comes from the Latin word for “oyster” because ostrovegans are vegans who eat oysters.
Almost all ostrovegans are also comfortable eating mussels, and many of them also eat scallops and clams.
All these simple animals are types of bivalve mollusks: They each have a two-part shell that hinges around a soft invertebrate body inside. Therefore, most ostrovegans can also be called bivalvegans.
The logic behind being an ostrovegan is that bivalves do not have a central nervous system and therefore are unlikely to experience pain in the way we think of it. But I’ll dive into more detail about this below because not everyone agrees.
Bivalves also happen to contain some nutrients that could potentially be helpful to a vegan diet, especially vitamin B12, which most vegans only get through supplementation.
When you put these facts together—(1) bivalves probably don’t feel pain and (2) bivalves contain nutrients that could help vegans—this is the logic behind why some vegans are okay with eating bivalves, even though they’re animals and vegans do not eat animals.
Understandably, some vegans disagree strongly with this ostrovegan movement. They say veganism is about not eating animals and bivalves are animals—so vegans shouldn’t eat bivalves, period. This is an argument from definition.
Another line of argument against ostroveganism is to say that we simply don’t know enough to be certain whether bivalves feel pain, so we should be cautious and not eat them for that reason.
Different Levels of Ostrovegans
Even within the group of “ostrovegans” there are some distinctions to be made. Some ostrovegans only eat oysters and mussels, whereas other ostrovegans also include clams and scallops.
The key distinction here is that oysters and mussels are sessile (they just sit there), whereas clams and scallops are a bit more motile (they move around).
The sessile versus motile distinction is relevant for ostrovegans because we have more reason to believe that sessile animals do not feel pain.
Think about it: If an animal felt pain but was not capable of moving, what evolutionary purpose would that serve? I’ll cover this point a bit more in-depth, with some sources, below.
Anyway, ostrovegans who only eat oysters and mussels may not be comfortable going by the term “bivalvegans,” as the group “bivalves” also includes those motile bivalves (clams and scallops) which they also exclude from their diet.
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Do Bivalve Mollusks Feel Pain?
Bivalve mollusks such as oysters, mussels, clams, and scallops do have nerves, but they do not have brains or any other central nervous system. So they do react to threats… but it may just be more like a nerve reflex.
When you accidentally touch your hand to a hot stove, you have a nerve reflex that pulls your hand back from the stove before you actually feel any sensation of pain. And the idea is that, without your brain, the pain would never happen—it’d just be a reflex.
When those reflexes happen, the nerves are firing but it does not require a brain. On the other hand, pain as far as we understand it does require a brain
“Nociception” vs Pain
“Nociception” refers to this kind of reflex without necessarily having any subjective experience of pain. The issue of nociception vs pain also comes up in discussions of whether bees and other insects feel pain.
If our basis for vegan ethics is actually the fact that we don’t want to cause suffering for other animals, then it is relevant to ask which animals actually can suffer!
Of course, not all vegans are strictly focused on reducing suffering—there are different approaches to vegan ethics, as I explained in this post. But generally, reducing pain is what matters—not reducing nociception.
Sessile Bivalves vs Motile Bivalves
As I mentioned above, some ostrovegans are okay with eating bivalves that are sessile (unable to move) but not okay with eating bivalves that are motile (able to move).
One of the best sources on this sessile vs motile bivalve distinction and how it relates to veganism is Diane Fleischmann in her article “The Ethical Case for Eating Oysters and Mussels.”
Fleischmann first mentions the simple point that there would be no evolutionary reason for sessile animals to experience pain because they are unable to move away from the threat.
Fleischmann also addresses another concern: Since bivalve mollusks are closely related to other mollusks like squid who are motile and do have brains, maybe there could be a leftover capacity for pain in bivalves which came from ancestor species?
But Fleischmann points out: “Pain is biologically expensive.” Feeling pain requires more calories to feed tissue capable of sensing and distinguishing helpful stimuli from harmful stimuli. Pain also distracts from other impulses in an organism that are needed to survive.
So even if a species originally had an ability to feel pain, Fleischmann argues that this capacity to feel pain is likely to have been lost through evolution in a sessile species. This is because pain would only have been a disadvantage to those animals unable to move.
Peter Singer on the Ethics of Eating Sessile Bivalves
Peter Singer’s 1975 book Animal Liberation is one of the most classic and influential texts in animal rights philosophy. It had a big influence on the vegan movement. And it does contain some mention of bivalves.
In the original 1975 version of Animal Liberation, Singer argued that eating sessile bivalves should be allowed as part of a vegan diet. This is because of the same reasons listed above (lack of a central nervous system).
Then in later editions of Animal Liberation, Singer made an edit, no longer endorsing the consumption of sessile bivalves. In those later editions, he simply says we don’t know enough about their ability to feel pain.
Research on Whether Mollusks Feel Pain
I found one major study in the ILAR Journal (ILAR = Institute for Lab Animal Research) looking at pain in mollusks and the animal welfare implications.
If you just read the abstract of the study, you’d definitely get the impression that there is considerable uncertainty about whether mollusks feel pain—but keep in mind, the abstract is talking about mollusks overall, not bivalves specifically.
Here’s a quote from the abstract (bolded emphasis is mine):
“Few studies have directly addressed possible emotionlike concomitants of nociceptive responses in molluscs. Because the definition of pain includes a subjective component that may be impossible to gauge in animals quite different from humans, firm conclusions about the possible existence of pain in molluscs may be unattainable. Evolutionary divergence and differences in lifestyle, physiology, and neuroanatomy suggest that painlike experiences in molluscs, if they exist, should differ from those in mammals. But reports indicate that some molluscs exhibit motivational states and cognitive capabilities that may be consistent with a capacity for states with functional parallels to pain. We therefore recommend that investigators attempt to minimize the potential for nociceptor activation and painlike sensations in experimental invertebrates by reducing the number of animals subjected to stressful manipulations and by administering appropriate anesthetic agents whenever practicable, welfare practices similar to those for vertebrate subjects.” (source)
So when you read this abstract, I feel like it’s understandable to just say we should avoid eating them just in case. But this research was about mollusks in general.
The researchers in that same study took a closer look at bivalves specifically, too.
Research on Whether Bivalve Mollusks Feel Pain
Here, the researchers address the behavior of motile bivalves (clams and scallops) in response to threats:
“Clams and scallops have simple eyes and chemosensory organs located along the periphery of the mantle and they initiate escape swimming if a threat is detected, thus some integration of information and basic decision making occurs.“
This study also mentions that previous research has found opioid receptors and endogenous opioids in blue mussels (Mytilus edilus) but that this finding is controversial.
If accurate, the presence of opioid receptors and endogenous opioids (opioids produced in the body) could suggest a capacity for feeling pain. But I’m assuming these elements could still just be vestigial (leftover from an ancestor) and not actually suggesting that mussels feel pain.
Overall, the researchers drew more conclusions about the animal welfare implications for whether higher mollusks, like cephalopods, can feel pain—they didn’t say as much about bivalves.
In the end, it seems difficult to infer what bivalve mollusks actually experience because their bodies and lives are so much different from our own.
Nutritional Benefits of Eating Bivalves
All of this debate about whether bivalves can feel pain would be pointless if there weren’t some great potential benefits for vegans eating bivalves. So that brings us to discuss the nutritional benefits.
Fully vegan diets can be very healthy for most people. But there are certain nutrients which are a little more difficult to get on a vegan diet or require more thoughtfulness and preparation.
Probably the biggest nutritional hole in veganism is vitamin B12. Long-term vegans need to supplement with vitamin B12 since it is typically only found in animal foods.
Oysters, clams, and other bivalves offer a potential source of vitamin B12, which may even be more bioavailable compared to a sublingual B12 supplement. And indeed, some ostrovegans adopted their diet specifically for the vitamin B12 found in bivalves.
Bivalves also provide protein and several other nutrients. Three of these nutrients are omega-3 fatty acids, zinc, and heme iron (the iron found in blood and animal foods), which is more readily absorbed than the non-heme iron found in plants.
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So, if you’re considering oysters for the B12 or omega-3’s, I might just suggest checking out a good multivitamin first, particularly Future Kind. That’s my personal solution. Read my full review here.
Going Ostrovegan to Fix Health Problems on a Vegan Diet
It is difficult to assess how many of the vegans who quit for health reasons actually needed to eat animal products such as bivalves to improve their health.
Many people who have struggled nutritionally on a vegan diet could likely have fixed the issue with supplementation, switching the focus to different vegan food groups, or just adding specific vegan foods.
Still, if you’re struggling with health issues on a vegan diet, I think it makes sense that bivalves could provide the nutritional fix you need without reverting to a completely non-vegan diet. Just go ostrovegan.
I think it absolutely makes sense if (1) you believe that veganism is about reducing suffering, (2) you believe that bivalves don’t suffer, (3) you think adding bivalves will make an otherwise vegan diet nutritionally sound for you, and (4) eating bivalves doesn’t gross you out!
Environmental Impact of Farming Bivalves
Most vegans care about the environmental impact of their diet as well, not just the pain experienced by individual animals. So how do bivalves hold up when it comes to environmental impact?
Oysters, mussels, and clams are all typically farmed, not wild-caught. These bivalve farms have actually received very favorable ratings from environmental groups such as the Environmental Defense Fund.
Scallops, on the other hand, are more often wild-caught. The way that scallops are collected from the wild typically involves bycatch, where other animals accidentally caught and killed as a side effect. So scallops are not as sustainable as other bivalves, generally speaking.
Is Bivalve Farming More Sustainable Than Plant Farming?
An interesting point when discussing the environmental impact of bivalve farming is that many plant foods are actually quite unsustainably produced, and vegans are fine with eating those foods.
In my post about whether vegans should eat organic food, I disgust some of the major environmental problems with both conventional and organic farming. So it’s not like vegan food is always great for the environment.
Many people have pointed out that, even with the most sustainable plant farming, small animals such as field mice are killed.
Given that field mice are much more likely to experience pain than bivalves, this suggests bivalve farming may actually cause less suffering than a lot of plant farming does.
So overall, it seems that eating bivalves is not typically bad for the environment, with the exception of scallops.
But whatever your conclusion is, you have to admit it’s an interesting conversation. It’s fascinating to look more deeply at the reasons why something should be considered vegan-friendly or not—rather than just accepting what you’ve heard from others on face value.
Mercury Levels Found in Bivalves
Some people may also be concerned with the mercury levels found in bivalves. Indeed, mercury levels are a common concern for any seafood options.
However, this study found that mercury levels found in 8 different mussel species were all relatively low.
The study concluded that mercury levels in mussels, and other bivalve mollusks, too, are not likely to cause adverse effects for consumers.
Should You Just Call Yourself “Vegan” if You Eat Mussels and Oysters?
Some people believe not only that it makes sense to be an ostrovegan but also that the definition of “vegan” itself should be expanded to include the consumption of bivalves.
Really this debate comes down to what the word “vegan” means.
Does being vegan mean that you don’t eat animals? Or does it mean that you don’t eat sentient animals? Or does it mean something else entirely?
The Definition of Veganism vs the Point of Veganism
When debating whether it’s “vegan” to eat oysters and mussels, some people will point out that sessile bivalves might as well be categorized as plants for all ethically relevant purposes.
By continuing to exclude sessile bivalves from a vegan diet, are you honoring the mere definition of “animal” above what actually matters more—sentience?
Vegans eat plants. Vegans eat yeast. These things are alive, too, but we are okay with eating them. We say it’s okay to eat them because they are not animals—but isn’t the real reason because they aren’t sentient?
And so, what happens when there are non-sentient animals? And how do we know for sure whether they are sentient? Where is the responsible place to draw the line?
Should You Eat Oysters and Mussels as a Vegan?
These are all ongoing debates. So when considering your own vegan diet and whether you should eat bivalves, make the decision that feels right to you.
Nobody is the true authority on this. Look at the data yourself and decide what you believe. In the end, as long as you feel that you’re making the right decision for yourself, that’s what matters.
It doesn’t matter what other vegans on a message board somewhere online think. It doesn’t matter what PETA thinks necessarily. It just matters that you’re doing your best to be true to what you believe in.
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