Are oysters vegan? Do bivalves feel pain and can you eat them on a vegan diet?

As a vegan, when it comes to eating animals it’s an open and shut case. But what if the animal doesn’t have a face or a centralised nervous system, and is often argued to be more plant-like than animal-like?

“Are oysters vegan?” is not a trick question. Oysters and other bivalves, such as clams and mussels, are often excluded from the definition of ‘animals’ – due to the simple fact that they lack a brain – and heated debate is resurging regarding whether vegans should or shouldn’t eat them.

• Why do some people consider oysters to be vegan?
• What are bivalves?
• Do bivalves feel pain?
• Are oysters environmentally friendly?
• Are oysters a good source of omega 3?
• Vegan alternatives to oysters and seafood
• So, are oysters vegan?

What are oysters?

Oysters are bivalve molluscs which grow and develop all around the world in saltwater. Oysters tend to live in shallow water, in places like estuaries, rock pools, and on piers.

Because they have developed in many different types of locations globally, there are a variety of molluscs that fall under the label ‘oyster’ in all sorts of shapes and sizes. Unfortunately for the oysters, many of them are harvested as food for humans – often considered a delicacy – while others are harvested for their pearls.

Oysters tend to have a rocky, frilly look which can vary greatly between species. Because of their craggy nature, the reefs and waterbeds they inhabit are provided with plenty of safe hiding places for small marine animals.

All oysters have gills, which are not only used for breathing. Oysters are filter feeders, so the water they draw over their gills is filtered to extract particles to use as food, which also helps to clean the water in the oysters’ environment.

Why do some people consider oysters to be vegan?

It is a common belief that oysters are not sentient and cannot feel pain due to their lack of a brain and centralised nervous system.

Due to this belief, and oysters’ lack of a face and any easily anthropomorphised features, many people who would otherwise follow a fully plant-based lifestyle, may feel justified in including oysters in their diet.

Others, particularly those who follow a vegan diet for environmental reasons, consider oyster farming to be a sustainable practice due to the oysters’ filtration of the water and the assertion that oyster farming positively impacts the environment.

However, while oyster beds do good for the ocean and coastlines, artificial cultivation and over-farming can still cause harm in the long run.

Competition for natural resources with local marine life can impact biodiversity, while mass harvesting of oysters can cause environmental damage through the removal of nutrients from the marine ecosystem.

What are bivalves?

Bivalves are classed in the animal kingdom as ‘molluscs’.

There are over 120,000 species of molluscs and while some display their abilities to make conscious decisions, others are far more sedentary; with decentralised nervous systems that in some cases react to stimuli more closely to the ways in which plants do, rather than animals.

Bivalve molluscs are easily recognisable by their external two-part hinged shells, connected by flexible ligaments that encase and shield their soft-bodied vulnerable innards. These include shellfish, such as clams, cockles, oysters, mussels and scallops, that use their gills to both breathe and feed.

Most bivalves live by filtering water-borne food particles through their gills – a type of filter feeding similar to whale sharks, basking sharks and rays.

Do bivalves feel pain?

While research into the positive role bivalves play in aquatic environments is clear, when it comes to the question of sentience, the waters get far murkier. Generally, being self-aware, creating thoughts and feeling pain are linked to centralised nervous systems, controlled by the brain.

So, for some people it follows that if an animal doesn’t have a brain, they are incapable of thoughts, feelings and emotions – especially those connected with pain.

However, despite decades of scientific study on the sentience of fish (who do have brains) there is still a refusal by some people to accept their capacity to have a level of awareness or cognitive ability comparable to our own.

While it is true that many non-human animals don’t scream out in pain, they do react to the world around them and activate their pain receptors (nociceptors) in response to discomfort. It is how humans interpret this that is the problem.

Most bivalves have a decentralised nervous system consisting of three-paired bilaterally symmetrical ganglia; cerebral, pedal and visceral. These are connected by nerve fibres and function like relay signals to create responses; moving, breathing, feeding, etc.

Bivalves can therefore detect and respond to threats and may well experience a feeling of stress in the presence of predators and close up their shells. As one indicator of sentience, it would seem logical to assume such decision-making is enough of an argument against eating them.

Understanding pain and how pain is felt across species is difficult, especially when studying non-human animals that are so far away from humans on the evolutionary scale.

Nevertheless, it would be wrong to underestimate response measures at the neural and behavioural level and centralised nervous systems cannot be the only feature that distinguishes what vegans should and shouldn’t eat.

Are oysters environmentally friendly?

In straining microscopic organisms through their gills to eat, oysters and bivalves play an important role in removing waste material, harmful organic matter and excess nitrogen from the water column.

As large volumes of water pass through their gills, phytoplankton, zooplankton, algae and various different nutrients are trapped and transported to their mouths, whereas waste is removed by their nephridia organs.

These organs function like kidneys and release inedible matter like grit as pseudofaeces – rejected particles wrapped in mucus that haven’t passed through the digestive tract.

By creating this natural filtration system through feeding, bivalves are often described as ecosystem-engineers. Although nitrogen is an essential nutrient for plants and animals, too much boosts the growth of algae, which can overwhelm waterways and marine ecosystems; starving them of oxygen and leading to aquatic dead zones.

Shellfish remove excess nitrogen by incorporating it into their shells and tissue as they grow. Oysters can each filter up to a staggering five litres of water an hour and therefore have a huge impact on cleaning up pollutants!

Are oysters a good source of omega 3?

While oysters and other bivalves can be considered effective sources of omega-3 fatty acids – something a lot of vegans worry about in their diets – they are not the only option.

Omega-3 s are a type of polyunsaturated fat our bodies need for brain development¹ and to regulate inflammation², but are unable to make. As well as reducing cholesterol build-up in our blood vessels, they also have a stabilising effect on heart rates³ and are therefore vital to good health.

Interestingly, fish don’t produce their own omega-3 either; they get it from the algae in their diet. It follows then that by consuming algae-based vegan supplements – grown in controlled conditions away from marine environments – it is possible to get what we need free from the pollutants, polychlorinated biphenyls, dioxins and mercury found in fish, fish products (including fish oil supplements) and shellfish.

Bivalves may also be a source of the winter vomiting bug norovirus, which they accumulate in contaminated seawater.

Healthier, plant-based sources of omega-3 include ground flaxseeds, chia seeds, hemp seeds, rapeseeds and their oils as well as walnuts.

Algae-based supplements are also an option to those who struggle to include enough of the seed- and nut-based sources in their diet.

Vegan alternatives to oysters and seafood

When it comes to oyster alternatives, options for vegans are limited. However, seafood alternative company Pearlita Foods has used cell-based technology to create a prototype alternative-oyster that looks and tastes like the real deal.

Flavoured with a base of mushroom and seaweed to give it a “pure, delicate, and authentic ocean flavor”, its vegan oyster alternative comes in recycled oyster shells from restaurants.

While there aren’t anywhere near as many seafood or oyster alternatives on the market as there are vegan burgers, sausages, and chicken products, seafood fans aren’t left completely lacking in options.

Some restaurants, such as Amsterdam vegan restaurant Vegan Junk Food Bar, offer plant-based versions of shrimp, calamari, and other seafood that can help to curb cravings.

At home, there are plenty of ways to make your own bivalve alternatives. You could use King oyster mushrooms to make vegan scallops, or leave the clams out of your soup by making a vegan corn chowder.

So, are oysters vegan?

So, are oysters vegan? Ultimately, no, because oysters are living, breathing organisms that can react to the world around them.

Oysters are beneficial to the ocean environment so, while it is ideal to have plenty of them living in the waters around us, over-farming and excessive harvesting of oysters can do more harm than good overall.

The best thing is, due to the beautiful array of nutrients and flavour available in a plant-based diet, eating bivalves is not necessary at all in maintaining a tasty, well-balanced diet that’s kind to animals, the planet and our health.

Oysters and other bivalves are essential for the health of the ocean. Discover how oceans can help the planet.

Featured photo © Gulnara Dautova via Getty Images

References:

1. Dighriri IM, Alsubaie AM, Hakami FM, Hamithi DM, Alshekh MM, Khobrani FA, Dalak FE, Hakami AA, Alsueaadi EH, Alsaawi LS, Alshammari SF, Alqahtani AS, Alawi IA, Aljuaid AA, Tawhari MQ. (2022) Effects of Omega-3 Polyunsaturated Fatty Acids on Brain Functions: A Systematic Review. Cureus. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9641984/
2. Simopoulos AP. (2022) Omega-3 fatty acids in inflammation and autoimmune diseases. Available at: https://pubmed.ncbi.nlm.nih.gov/12480795/
3. Khan, SU., Lone, AN, Khan MS, Virani SS, Blumenthal RS, and Nasir, K. (2021) Effect of omega-3 fatty acids on cardiovascular outcomes: A systematic review and meta-analysis. Available at: https://www.thelancet.com/journals/eclinm/article/PIIS2589-5370(21)00277-7/fulltext