Are Fish Sentient?

For those of you who are just reading my content for the first time, for a good amount of my adult life I have been living with and caring for small species of benthic sharks. What started out as a hobby turned into rescuing, rehabilitating and re-homing over 100 sharks with my good friend Matt Heyde. I have also conducted several breeding projects in an aquaculture facility for several years and bred thousands of Seahorses.

Aside from all of the biology, sciencey stuff that they taught me, I also learned that they very much are sentient beings. And it turns out that there have been quite a few different studies that suggest this as well. Let’s take a look at a few of these studies and then I’d love to hear what you think – whether or not you think fish are sentient beings in the comments section below.

First let’s define Sentient: able to perceive or feel things. This can be from an emotional perspective as well as from a physical perspective.

Let’s address the physical part first.

Do Fish Feel Pain?

A brief history on this long debated question:


English philosopher Jeremy Bentham shared his idea that has been central to debates about animal welfare ever since: “When considering our ethical obligations to other animals, the most important question is not, ‘Can they reason? nor, Can they talk? but, Can they suffer?'” This question was debated for a very long time.


Writer and fisherman Ed Zern explained in an issue of Field & Stream that:

“Fish don’t feel pain the way you do when you skin your knee or stub your toe or have a toothache, because their nervous systems are much simpler. I’m not really sure they feel any pain, as we feel pain, but probably they feel a kind of ‘fish pain.’ Ultimately, whatever primitive suffering they endure is irrelevant, because it’s all part of the great food chain and, besides, if something or somebody ever stops us from fishing, we’ll suffer terribly.”


The Medway Report, commissioned by the Royal Society for the Prevention of Cruelty to Animals (RSPCA) and published in 1980, concluded that:

“In the light of evidence reviewed … it is recommended that, where considerations of welfare are involved, all vertebrate animals (i.e., mammals birds, reptiles, amphibians and fish) should be regarded as equally capable of suffering to some degree or another, without distinction between ‘warm-blooded’ and ‘cold blooded’ members.”


During a discussion between Penn State University biologist Victoria Braithwaite and head of the Scottish Fishermen’s Federation, Bertie Armstrong , Bertie dismissed the notion that fish deserve welfare laws as “cranky” and insisted that “the balance of scientific evidence is that fish do not feel pain as we do.”

To which Braithwaite refuted that:

“It is impossible to definitively know whether another creature’s subjective experience is like our own. But that is beside the point. We do not know whether cats, dogs, lab animals, chickens, and cattle feel pain the way we do, yet we still afford them increasingly humane treatment and legal protections because they have demonstrated an ability to suffer.”

In the past 15 years, Braithwaite and other fish biologists around the world have produced substantial evidence that, just like mammals and birds, fish also experience conscious pain. “More and more people are willing to accept the facts,” Braithwaite says. “Fish do feel pain. It’s likely different from what humans feel, but it is still a kind of pain.”

So what kind of pain is it exactly?

Fish have neurons known as nociceptors, which detect potential harm such as:

  • high temperatures
  • intense pressure
  • caustic chemicals

Fish can also produce the same opioids (the body’s innate painkillers) that mammals do. Their brain activity during injury is comparable to that in terrestrial vertebrates as well. So the answer is yes, fish feel pain. With more and more studies being conducted we are getting closer to understanding more more about their ability to feel pain and how that translates to our perception of pain.

The second element to the definition of a sentient being is being able to feel emotions.

Do Fish Have Emotions?

In 2017 Portuguese researchers found that fish do exhibit emotional states which are triggered by their environment. In short, since fish can’t talk to us, there is no straightforward way to evaluate what they are feeling – since we can’t ask. From a more indirect approach, these scientists based their findings on changes in the fish’s behavioral, physiologic, neurologic and genetic changes.

Seam Bream
Image Source: PetGuide

For example, in one experiment The Portuguese biologists trained Sea Bream under both favorable and adverse conditions; these conditions were expected to trigger an emotional state. They then analyzed this emotional response by measuring the levels of cortisol, a stress hormone and seeing what brain areas become activated. Researchers also tracked fish interaction and overall behavior to assess their response. These responses were then backtraced to the Sea Bream’s emotional states.

“Our data supports the occurrence of emotion-like states in fish that are regulated by the individual’s perception of environmental stimuli” the study reads. “They showed not only that fish do get feelings, but this study might give us a better understanding of how emotions came to be in the first place. Since fish represent a different evolutionary branch than tetrapods, this might indicate that emotions emerged before the two groups separated. Alternatively, it could be a case of convergent evolution.” – ZME Science

“This is the first time that is shown that fish can trigger physiologic and neuromolecular responses in the central nervous system in response to emotional stimuli based on the significance that that stimulus has for the fish”, says study author Rui Oliveira. The researcher explains that “the occurrence of the cognitive assessment of an emotional stimulus in fish means that that this cognitive capacity may have ‘computational’ requirements simpler than what has been considered until now, and may have evolved around 375 million years ago.”

Anyone who has had an aquarium for many years can tell you that each of their fish – and even their invertebrates – have their own individual personalities. An aquarist can also tell if a fish are in a bad mood, not feeling well or are upset with another fish in their aquarium. While the layman won’t report this information in the form of specific chemical measurements, etc. I think that our very own sentient abilities can help us to detect if another being on this planet is sentient or not with enough observation.

And now I’ll pass the question off to you – what do you think? As fish sentient beings? Let me know your thoughts in the comments below.

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