Do oysters feel pain? Are they vegan?

The objection

“Oysters and mussels have no brain and can’t move, so eating them harms nothing. ‘Bivalvegans’ are right, and it proves the line is arbitrary.”

The answer

By the Vegan Society’s definition oysters and mussels aren’t vegan, since it describes a vegan diet as one that avoids shellfish along with fish and insects [1]. The objection still has a point. Bivalves, the group that also takes in clams, cockles and scallops, have no brain in the sense that vertebrates have one [2], only a few clusters of nerve cells, called ganglia, linked by nerve cords in a layout that a 2020 study of mussel nerves described as relatively simple [12]. People who call themselves bivalvegans have a better case than most critics of veganism, though it rests on a gap in the research rather than a finding.

Do oysters and mussels feel pain?

Nobody knows: a preliminary scan of the literature by Wageningen Marine Research in the Netherlands, which searched one database, Scopus, in 2022, found no study that directly tested whether bivalves are sentient [3]. The scan was commissioned by the Dutch shellfish industry’s quality foundation and a Dutch fish-protection foundation. It did turn up a few studies of behaviour and nerve chemistry which, in the report’s words, “indicate that bivalves might indeed be sentient”, though it judged that evidence very limited and the gaps in knowledge large [3]. Evaluating those studies in depth was beyond what the sponsors had asked for, so the authors recommended a full literature review [3].

In one of them, from 2022, blue mussels that had met a parasite’s larvae before filtered less water than mussels new to them when the larvae returned, and so caught fewer infections, though the authors could not tell whether the mussels had learned to link a cue with the threat, had simply grown more sensitive to it, or had changed in some other way [4]. Mussels shut their shells when they sense the larvae [4], and a scallop has up to 200 eyes, each focusing light with a mirror (Palmer et al. 2017) [5].

Reacting to harm is still some way from feeling it. One hypothesis about how consciousness evolved, proposed by Feinberg and Mallatt, draws its criteria from a survey of brain anatomy and behaviour across a broad range of animals. In the summary that Taiz and colleagues gave in 2019, the only animals meeting those criteria were vertebrates, arthropods such as insects and crabs, and cephalopods such as octopuses, which leaves bivalves out [6]. A 2011 review by Crook and Walters, covering how several groups of molluscs detect and respond to injury, judged that firm conclusions about pain in molluscs may be unattainable, and saw the possibility of painlike states in at least some molluscs, those with more complex nervous systems [7].

Do oysters prove the vegan line is arbitrary?

Oysters don’t prove the line arbitrary, because a hard case at the edge of a line shows where it runs, and this one runs along sentience, the capacity to feel. The New York Declaration on Animal Consciousness, launched at New York University in 2024, finds at least a realistic possibility of conscious experience in all vertebrates and in many invertebrates, at minimum cephalopods, decapod crustaceans and insects; bivalves are not among the groups it names [9]. UK law stops shorter still. The Animal Welfare (Sentience) Act 2022 covers every vertebrate except humans, every cephalopod mollusc, such as octopuses and squid, and every decapod crustacean, such as crabs and lobsters, but no insects or bivalves, though ministers can add invertebrates by regulations [8]. However the oyster question is settled, it leaves the cow, the pig, the chicken and the fish where they were.

Why give oysters the benefit of the doubt?

Oysters deserve the benefit of the doubt because the two possible mistakes are nowhere near equal in cost. If bivalves feel nothing, a vegan who leaves them out gives up less than it might seem. A 2021 analysis in Nature did find the lowest environmental impacts of any aquatic food in farmed bivalves, but it found them in farmed seaweeds as well [13]. The vitamin B12 that plants lack comes reliably from fortified foods or a supplement, and zinc from beans, nuts and seeds, though the body absorbs less of it from plants than from animal foods [14]. If bivalves can suffer, eating them causes suffering that was easy to avoid.

Veganism, in the Vegan Society’s definition, seeks to exclude exploitation of and cruelty to animals “as far as is possible and practicable” [1], and skipping shellfish is about as practicable as it gets. Crook and Walters (2011) urged the same caution in the laboratory, recommending that researchers working with invertebrates put fewer animals through stressful procedures and give anaesthetics whenever practicable, much as they would for vertebrates [7].

Are pearls vegan?

Pearls aren’t vegan either, since the Vegan Society’s definition excludes exploiting animals “for food, clothing or any other purpose” [1]. In pearl oysters, the grafting method used to culture pearls, developed in the early 1900s and little changed since, sacrifices a donor oyster for a piece of its mantle tissue, which is implanted in a host oyster to form a pearl around a bead (Kishore & Southgate 2015) [10]; a 2005 study found that donors can regrow the tissue and need not be killed [11].