This is a post I first wrote in May of 2013. This was the most popular post on Sentientist.org.
In May of 2008 I became vegan or…well, ostrovegan. In this blog I officially come out of the closet, err, shell. I am almost sure that cultivated mussels and oysters are ethical to eat. I argue eating these animals is completely consistent with the spirit if not the letter of ethical veganism and the tenet of causing less harm with our consumer choices1. This blog is on bivalve sentience/ability to suffer; for further arguments, including nutrition arguments, see this second blog.
Are mussels and oysters sentient?
Dividing organisms up into types, or cladistics, is tricky business. Nature did not develop in a way that fits neatly into categories. Dividing up organisms on the basis of sentience, or the ability to suffer, may be even trickier. So, is there any evidence that mussels and oysters don’t suffer?
Argument 1- Oysters and Mussels are not motile
Let me start with a perspective derived from evolutionary theory about how organisms are designed. The function of pain is to help an organism avoid stimuli that may cause them bodily harm. Organisms that are sessile, or unable to move, cannot escape pain and thus there really isn’t any adaptive reason for them to feel pain. Sessile bivalves can open and close their shells but this is as simple an action as plants who close in the presence of noxious stimuli. For a variety of reasons I won’t go into here, plants don’t feel pain. The definition of vegan typically includes not consuming anything of animal origin. And, as animals are most often motile and thus have an adaptive reason to feel pain, this makes sense.
But, mussels and oysters are closely related to other species (e.g. scallops, squid) who are motile and might, by my logic, can feel pain, is it possible that they have some leftover capacity to suffer from a common ancestor?
This is very unlikely because pain is biologically expensive. 2 In order to feel pain an organism must have to have a sensory system capable of differentiating ‘good’ or adaptive stimuli from ‘bad’ or harmful stimuli. On top of this, the experience of pain is often damaging in and of itself. Finally, in order to facilitate moving away from pain an organism’s priorities change. For instance, pain reduces hunger and the desire to mate. Given that no system is perfect and there is always some rate of misfiring, a sessile organism that experiences pain would get all the harm and none of the benefit of moving away from painful stimuli and thus be at a disadvantage.
-Oysters and mussels have a larval stage that is motile (see this and this). During this larval stage the animals react to stimuli and may even hitch a ride on fish to disperse more widely. Also, freshwater mussels (which are not commonly eaten by humans) are more motile and can move (albeit slowly). During the larval stage there are neurons present however “many of the larval neurons disappear after metamorphosis“. Both of these facts make me less confident in the motility argument but I still think the other arguments below stand on their own. /Addendum
Argument 2- Oysters and mussels have rudimentary nervous systems and do not seem to use endogenous opiates or opiate receptors to inhibit pain
Translation: Bivalves have a very simple nervous system which is not aggregated in anything like a brain. Other invertebrates, like shrimp, show changes in behavior (e.g. grooming their antenna after injury) neurotransmitters or neural firing in response to injury, but previous studies have not shown this kind of response in bivalves.
My conclusion: Bivalves do not have hardware or response consistent with the ability to feel pain. Because they have no brain, or central processing unit for stimuli, there is no ‘there’, there. Just like a disembodied finger, there is no place for sensations to be aggregated into responses or changes in adaptive decision making.3
Many animals have opiate receptors, indicating they are making painkillers and regulating pain within their own nervous system. One way that animal pain is gauged is to administer opiates and see if it influences the behavioral response to pain (e.g.). There is some evidence that bivalves have opioids and opioid receptors but 1) there isn’t good evidence that bivalves have the genes that code for these receptors and 2) it seems that opiates are being used to signal the immune system not to regulate pain. To be honest this is the point on which I am least confident and on which science isn’t yet conclusive.
Argument 3- Eating cultivated oysters and mussels doesn’t doesn’t kill other (sentient) animals at a rate greater than agriculture
No food is completely deathless. When you eat plants or grains you are often supporting a system that kills insects and rodents, and displaces wild animals. Let’s say that you eat shrimps because you doubt that they are sentient. Even if you are on an invertebrate only diet, many species are dredged or netted which involves bycatch, or the deaths of many other organisms after they are harmed by being brought up out of the water and thrown in again. With shrimp, for instance, the rate of bycatch is enormous, sometimes up to 98% of what is caught is discarded, and much of this bycatch is vertebrates. Surely, eating animals that aren’t sentient could not be ethical if it involved significant numbers of deaths for animals that are sentient.
-The only dredging involved in cultivation is collecting spat, or the “seeds” that become mature mussels, however rope cultured mussels don’t generally involve dredging for spat but collecting it on the surface thus not displacing other organisms.
-Oyster and mussel cultivation has been endorsed as good for water quality (e.g. they filter out excess nitrogen) doesn’t involve antibiotics and doesn’t involve killing other animals to feed to them as is the case with farmed fish (e.g. this source is not objective but details many potential environmental benefits from shellfish aquaculture).
-Eating oysters and mussels may involve less other animal death and displacement than eating grains or soy (although I have yet to do a proper calculation on this).
In the next blog I’ve argued that including oysters and mussels as ethically acceptable on a vegan diet undermines naturalistic, nutritional and emotional arguments against veganism thus promoting ethical eating. I’ll also speculate about whether there would be fewer vertebrate eating ex-vegans if ostrovegan was considered an ethically acceptable in a vegan diet.
2– Brains, often needed in motile organisms, are also biologically expensive:
3–David Pearce, who disagrees with me and thinks that we should give oysters and mussels the benefit of the doubt (partly because of possible opiate receptors) has conceded this:
“Just as I think it’s possible some of our peripheral ganglia feel phenomenal pain that is inaccessible to the CNS (cf. how one sometimes withdraws one’s hand from a hot stove before one feels the searing pain) it’s possible mussels and oyster ganglia feel something similar. But rights for individal nerve ganglia clearly can’t be high on our list of moral priorities”