Sentience in aquatic animals: FAQ

March 29 is the 9th World Day for the End of Fishing and Fish Farming. Aquatic animals constitute the largest number of animals killed by humans each year. Estimates suggest tens of trillions of individuals, including fishes, crustaceans, and cephalopods, are caught and killed every year. Let’s reflect on this atrocity and how to address it. Let’s also clear up any questions you may have about these issues through our FAQ.

Have you noticed that aquatic animals get much less attention than land animals by the majority of humans? This is true both in scientific research and in everyday situations. Even though oceans, lakes, and rivers cover most of our world, we don’t think much about the experiences and feelings of the animals living there. But there are strong reasons to believe that many aquatic animals can feel and suffer, just like the animals we’re more familiar with on land.

Understanding these issues helps us see how our actions and omissions affect billions of these animals, and what we might do differently to reduce their suffering.

Frequently Asked Questions

Why should we care about aquatic animals?

For a long time, people thought only humans had the ability to feel, but science has proven this wrong. In 2012, a group of scientists finally formalized the scientific consensus on nonhuman animal sentience by signing the Cambridge Declaration on Consciousness.¹ The declaration states that many nonhuman animals have the brain structures needed for consciousness. In other words, they can feel pain and pleasure. More recently, in 2024, the New York Declaration on Animal Consciousness recognized that all vertebrates (including fishes) and many invertebrates (including aquatic animals) likely have conscious experiences.²

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Consider this:
If these animals can feel pain, pleasure, fear, or comfort, then what happens to them matters to them. Humans cause enormous harm to aquatic animals through fishing, pollution, habitat destruction, and other activities. Many of these harms could be reduced or prevented with relatively small changes to our behavior.

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How do we know if an aquatic animal is sentient?

While we can’t directly experience what another being feels, scientists look for certain signs.

Behavioral signs:

·⠀Avoiding things that might cause pain

·⠀Seeking out pleasant experiences

·⠀Paying special attention to injured areas

·⠀Learning from past experiences to avoid harm

·⠀Exploring their environment in ways that show curiosity

·⠀Changing their behavior when given pain-relieving medications

For example, many fishes will actively avoid places where they’ve been harmed before.³ This isn’t just an automatic reaction – they’re showing signs of remembering a negative experience and making a decision based on that memory. When animals show these kinds of behavior, it suggests they’re experiencing something subjectively, not just reacting automatically.

Physical signs:

·⠀Although the nervous systems of many aquatic animals are very different from those of humans, they have something in common: a centralized nervous system with brains or nerve ganglia, which is where conscious experiences are generated. This includes cephalopods such as octopuses and crustaceans such as shrimps

·⠀Many fishes, mollusks, and crustaceans have nociceptors, which are special nerve receptors that detect harmful stimuli

·⠀Many aquatic animals produce natural substances that block pain

The combination of these physical features would be hard to explain if the animal couldn’t feel anything.

Fishes don’t have a neocortex like mammals do. Doesn’t that mean they can’t feel pain?

For a long time, scientists thought the neocortex (a part of the mammalian brain) was necessary for conscious experiences. Since fishes don’t have this exact structure, some people assumed they couldn’t feel pain.

However, newer research shows this assumption was wrong.⁴ Fishes have their own brain structures that serve similar functions.⁵ This is similar to how fishes don’t have lungs like humans do, but their gills allow them to extract oxygen from water – a different structure that serves the same vital function of breathing, but adapted to their aquatic environment.

Scientists now have a strong consensus that fishes can feel pain, even without a neocortex.

In addition, fishes have capabilities that seem to require awareness and subjective experiences.

·⠀Memory: Some fishes can remember negative experiences for nearly a year. Some of them avoid nets for up to 11 months after being captured, while salmons and carps avoid hooks for up to a year after being caught.

·⠀Problem-solving: Fishes like cichlids and freshwater rays can solve complex problems, showing flexible thinking.

·⠀Communication: Many fishes use visual signals, sounds, and chemical signals to communicate with each other. Catfishes produce sounds to talk to other catfishes, while tropical fishes use visual displays to establish hierarchies in their social groups.

Aren’t shrimps too simple to feel anything?

Many aquatic invertebrates (animals without backbones) also show strong signs of sentience. Let’s look at some major groups.

Crustaceans (crabs, lobsters, shrimps, krill)

·⠀They have nociceptors (pain receptors) and brain regions that process pain signals⁶

·⠀Shrimps pay special attention to injured areas of their bodies

·⠀Their behaviors show they can adapt to different situations to seek positive experiences and avoid harmful ones

·⠀A scientific report from the London School of Economics found enough evidence of sentience that the UK included decapod crustaceans in their Animal Welfare Act of 2022⁷

Cephalopod mollusks (octopuses, squids, cuttlefishes)

·⠀These animals have the most complex nervous systems of any invertebrates

·⠀Their brains have specialized areas for processing different types of sensory information

·⠀They have about 500 million cells in their central nervous system

·⠀This complexity allows them to learn, solve problems, and demonstrate what appears to be planning.

·⠀When injured, they show immediate responses and develop long-term sensitivity to touch

·⠀Octopuses give special attention to injured areas for extended periods

Other mollusks (clams, snails, sea slugs)

·⠀Even with simpler nervous systems, many have nociceptors that appear to function similarly to those in mammals

·⠀They can make long-term behavioral changes to avoid future harm

·⠀They demonstrate associative learning – they can connect certain situations with negative experiences and adjust their behavior

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Consider this:
Many crabs and lobsters are boiled alive while fully conscious. It takes several minutes for them to lose consciousness while boiling. They show signs of distress in this process like thrashing, struggling to escape, and losing limbs.

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If aquatic animals can suffer, why don’t people pay as much attention to them as land animals?

There are several reasons for this:

·⠀We don’t see them as often in our daily lives

·⠀Their environments are very different from ours

·⠀They often look and behave very differently from us

·⠀It’s harder to observe their behavior and reactions

·⠀There’s a widespread lack of knowledge about fish and other aquatic animal sentience

·⠀Cultural practices such as sport fishing are romanticized and normalize the killing of these animals

This lack of attention means less research on their experiences and less concern about their suffering. However, the fact that we have less of a relationship with them does not mean that they cannot feel what is happening to them.

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Consider this:
If a dog were treated the way we treat fishes or lobsters – being hooked through the mouth or being cooked alive – most people would consider it shocking.

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How many aquatic animals are killed for human consumption each year?

The numbers are staggering. While about 80 billion land animals (like cows, pigs, and chickens) are killed annually for food, aquatic animals are killed in much higher numbers:

·⠀Between 1.1 and 2.2 trillion fishes are killed each year⁸

·⠀Fish farms alone kill between 78-171 billion finned fishes yearly⁹

·⠀Fish farms also kill between 310-950 billion crustaceans (crabs, shrimps, etc.) annually¹⁰

It’s hard to get exact numbers because fishing industry statistics are typically measured in tons rather than counting individual animals. But even the approximate figures show us the magnitude of the plight of these animals.

Which animals die in the greatest numbers for human consumption?

Shrimps are by far the animals who are killed in the greatest numbers:

·⠀Approximately 25 TRILLION wild shrimps are caught annually

·⠀About 440 BILLION shrimps are killed on farms each year

To put this in perspective, the number of farmed shrimps is:

·⠀2.2 times the number of farmed fishes

·⠀2.7 times the number of farmed insects

·⠀6.9 times the number of farmed chickens

And wild-caught shrimp numbers are about 57 times higher than farmed shrimp numbers.

What happens to aquatic animals caught in the wild?

All fishing methods cause immense suffering to aquatic animals.

Trawling

Large nets are dragged along the ocean floor. As they’re pulled through the water, fishes suffer injuries when their bodies are dragged over rocks and debris, resulting in wounds, scale loss, and broken fins. The soft bodies of cephalopods (octopuses, squids) are especially prone to injuries and abrasions, and the shells of lobsters can crack and their antennae can break when they are dragged along the seafloor. When deep-sea fishes and crustaceans are quickly pulled to the surface in nets, they undergo rapid pressure changes that can cause their organs to burst, resulting in a painful death. Those who survive often die from suffocation, being crushed, or violent killing methods like being beaten to death.

Purse seine fishing

This method targets animals near the water’s surface. Nets are dragged forward, trapping everyone in their path. Animals experience extreme stress and often sustain injuries, especially to sensitive areas like the fishes’ gills. As the net closes like a purse and tightens, animals are crushed against each other, causing further injury and distress before they’re hauled aboard.

Drift nets

These are fine-mesh nets left floating in the water that indiscriminately catch all the animals that are there. Dolphins, sea turtles, and sharks can be trapped in one of these nets for days. These trapped animals struggle desperately to free themselves, causing cuts and injuries as they fight against the netting. Many experience suffocation, exhaustion, and extreme stress before they die or are pulled aboard fishing vessels.

Longline fishing

This technique uses thousands of hooks left in the water for long periods. Animals who take the bait or accidentally get caught suffer ripped skin in the mouth and body, fractures, and internal bleeding from the hooks. They experience prolonged distress while trapped, unable to escape as they struggle against the hooks that pierce their bodies, often for hours or days.

What conditions do aquatic animals face in farms?

Aquatic farms (also called aquaculture) generate suffering in ways that are different from wild capture but are very harmful to the animals.

Common killing methods on farms include:

·⠀Suffocation: Simply removing fishes from water, causing their gills to collapse (can take minutes to hours)

·⠀Live chilling: Placing live animals like fishes or shrimps in slurry ice until they freeze or suffocate (can take hours)

·⠀Stunning: Using electricity to supposedly render fishes unconscious before killing them (but they may only be paralyzed and still conscious)

In aquatic farms, animals suffer from extreme overcrowding and poor water quality. This causes high levels of stress (measurable by increased cortisol hormones), which can trigger aggressive behavior and self-harm (like eating their own limbs). All this can lead to a weakening of their immune systems and promote the spread of diseases.

Some farmed fishes like salmon and rainbow trout undergo genetic modifications, such as forced triploidy. Forced triploidy is a genetic modification that gives them three sets of chromosomes instead of the normal two, which increases their reproductive capacity. However, this modification causes substantial health problems.¹¹

For example, it can lead to decreased breathing capacity, decreased life expectancy, and various other health issues that impact them throughout their entire lives.

In many shrimp farms, a common practice is “eyestalk ablation,” where females have their eyes removed or crushed because it makes them reproduce faster. After this, shrimps show pain behaviors like rubbing wounds and making nervous movements.¹²

In some farms and restaurants, the claws of crabs and lobsters are often torn off, which can cause physiological stress and higher rates of infection. Sometimes they are restrained with tight rubber bands, which cause muscle atrophy and prevent them from eating properly.

What other risks do aquatic animals face, besides those caused by humans?

Aquatic animals face many natural sources of suffering. Some of them are:

Diseases

·⠀Bacterial infections like columnaris can cause skin lesions, ulceration, and difficulty swimming in some fishes

·⠀Viral diseases like hemorrhagic septicemia cause internal bleeding and death of fishes

·⠀In the wild, there’s no place to recover safely while dealing with illness

Environmental challenges

·⠀Cold-blooded animals are vulnerable to sudden temperature changes

·⠀Storms and tsunamis can cause injuries and make finding food difficult

·⠀Lobsters in warmer waters are more prone to shell disease

Predation

·⠀The constant fear of predators causes mental and physical stress

·⠀Animals that survive initial attacks often suffer severe injuries like lacerations and fractures

·⠀While some aquatic animals can regenerate parts, serious injuries often mean a slow, painful death or living in chronic pain

High juvenile mortality

·⠀Most aquatic animals produce many offspring with few survivors

·⠀A single salmon can lay 20,000 eggs, while cod and tuna can produce millions

·⠀In stable populations, only one offspring per parent typically survives to adulthood

·⠀Most die from cold, disease, predation, or starvation without ever eating a single meal

What can I do to reduce aquatic animal suffering?

Here are concrete ways you can help:

Personal Actions

1. Stop consuming aquatic animals

·⠀The most direct way to help is to stop eating fishes, shrimps, and other aquatic animals. Each time you choose plant-based alternatives, you’re reducing demand for practices that cause immense suffering.

·⠀Research plant-based seafood alternatives that are increasingly available in stores and restaurants.

2. Educate yourself and others

·⠀Share information about aquatic animal sentience with friends and family. Many people simply don’t know that fishes and aquatic invertebrates can feel pain or experience stress.

·⠀Challenge the romanticization of fishing and correct misunderstandings about the capacity of aquatic animals to suffer.

·⠀Use social media to spread awareness, not just around World Day for the End of Fishing and Fish Farming, but every day.

3. Speak up when you see misinformation

·⠀When you hear someone say “fish don’t feel pain” or “shrimp are too simple to suffer,” politely correct them with the scientific evidence.

·⠀Point out the double standard in how we treat aquatic animals compared to land animals (would we accept a dog being hooked through the mouth or boiled alive?).

Supporting larger initiatives

1. Support organizations working for aquatic animals

·⠀Donate to and volunteer with organizations specifically focused on ending fishing, fish farming, and finding ways to help aquatic animals.

·⠀Share the social media posts of organizations working to end or stop the spread of aquatic animal exploitation and other harmful practices like deep sea mining for minerals.

2. Advocate for legal protections

·⠀Support bills and policies that recognize aquatic animal sentience and provide legal protections. The UK’s inclusion of crustaceans in their Animal Welfare Act is one example of progress.

·⠀Support efforts to ban new forms of aquatic farming, such as octopus farms.

3. Support research

·⠀Back non-invasive scientific research that furthers our understanding of aquatic animal sentience and suffering.

·⠀Support research to help aquatic animals who are suffering from natural harms.

·⠀Help fund organizations working to develop alternatives to fishing and aquaculture.

Remember that the goal isn’t to make fishing or fish farming “more humane” but to end these practices entirely. Every sentient being has an interest in avoiding pain and continuing to live. When we recognize aquatic animals as individuals with their own experiences rather than as resources, the ethical path becomes clear: we must stop harming them.

Your individual choices matter, especially when combined with advocacy that can create systemic change. By addressing both your personal impact and working toward larger social and policy shifts, you can help reduce the immense suffering inflicted on trillions of sentient beings every year.

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Further readings

Acerete, L.; Balasch, J. C.; Espinosa, E.; Josa, A. & Tort, L. (2004) “Physiological responses in Eurasian perch (Perca fluviatilis L.) subjected to stress by transport and handling”, Aquaculture, 237, pp. 167-178.

Bae, S-H.; Tomoyuki; O.; Bong, J. K. & Wilder, M. N. (2013) “Alterations of pattern in immune response and vitellogenesis during induced ovarian development by unilateral and bilateral ablation in Litopenaeus vannamei”, Fish Science, 79, pp. 895-903.

Alanara, A.; Winberg, S.; Brannas, E.; Kiessling, A.; Hoglund, E. & Elofsson, U. (1998) “Feeding behaviour, brain serotonergic activity levels, and energy reserves of Arctic char (Salvelinus alpinus) within a dominance hierarchy”, Canadian Journal of Zoology, 76, pp. 212-220.

Barr, S. & Elwood, R. W. (2024) “Effects of acetic acid and morphine in shore crabs, Carcinus maenas: Implications for the possibility of pain in decapods”, Animals, 14 (11) [accessed on 5 March 2025].

Chandroo, K. P.; Yue, S. & Moccia, R. D. (2004) “An evaluation of current perspectives on consciousness and pain in fishes”, Fish and Fisheries, 5, pp. 281-295.

Chapman, P. A.; Cribb, T. H.; Flint, M.; Traub, R. J.; Blair, D.; Kyaw-Tanner, M. T. & Mills, P. C. (2019) “Spirorchiidiasis in marine turtles: The current state of knowledge”, Diseases of Aquatic Organisms, 133, pp. 217-245 [accessed on 14 January 2025].

Cutts, C. J.; Metcalfe, N. B. & Taylor, A. C. (2002) “Fish may fight rather than feed in a novel environment: Metabolic rate and feeding motivation in juvenile Atlantic salmon”, Journal of Fish Biology, 61, pp. 1540-1548.

FAO (2024) The state of world fisheries and aquaculture: Blue transformation in action, Rome: FAO [accessed on 25 February 2025].

McKay, H. & McAuliffe, W. (2024) “Pre-slaughter mortality of farmed shrimp”, Rethink Priorities, March, 12 [accessed on 29 February 2025].

Perazzolo, L. M.; Gargioni, R.; Ogliari, P.; Margherita, A. A. & Barracco, M. A. A. (2002) “Evaluation of some hemato-immunological parameters in the shrimp Farfantepenaeus paulensis submitted to environmental and physiological stress”, Aquaculture, 214, pp. 19-33.

Rose, J. D. (2002) “The neurobehavioural nature of fishes and the question of awareness and pain”, Reviews in Fisheries Science, 10, pp. 1-38.

Sainz-Hernández, J. C.; Racotta, I. S.; Silvie, D.; Hernández-López, J. (2008) “Effect of unilateral and bilateral eyestalk ablation in Litopenaeus vannamei male and female on several metabolic and immunologic variables”, Aquaculture, 283, pp. 188-193.

Sneddon, L. U.; Braithwaite, V. A. & Gentle, M. J. (2003) “Do fishes have nociceptors? Evidence for the evolution of a vertebrate sensory system”, Proceedings of the Royal Society B: Biological Sciences, 270, pp. 1115-1121 [accessed on 20 March 2025].

Waldhorn, D. R. & Autric, E. (2023) “Shrimp: The animals most commonly used and killed for food production”, Rethink Priorities, August, 11 [accessed on 30 January 2025].

Wendelaar-Bonga, S. E. W. (1997) “The stress response in fish”, Physiological Reviews, 77, pp. 591-625.

Zacarias, S.; Carboni, S.; Davie, A. & Little, D. C. (2019) “Reproductive performance and offspring quality of non-ablated Pacific white shrimp (Litopenaeus vannamei) under intensive commercial scale conditions”, Aquaculture, 503, pp. 460-466.

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Notes