Do fish have feelings? Scientists believe they’re getting closer to an answer

When scientists demonstrated a small tropical fish – the cleaner wrasse – could recognise itself in a mirror , Prof Culum Brown’s first thought was: “This is the coolest thing ever.”

Brown, an ecologist who researches fish behaviour and intelligence at Sydney’s Macquarie University, says the mirror self-recognition test – developed in the 1970s – is considered the gold standard for evidence of visual self-awareness in animals.

In the Osaka City University study , a small number of fish had a mark placed under their throats while under anaesthesia. When given a mirror, the fish oriented their bodies to see the mark, and tried to rub it off by scraping themselves on rocks.

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Primates, elephants and dolphins previously passed the test. But the results in fish proved so controversial it took five years for the paper to be published.

Even then, many scientists refused to accept the results.

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Brown says the response “shows beautifully” the bias against the idea of fish being intelligent – particularly when parts of the scientific community instead thought, “Shit! The mirror self-recognition test is broken.”

Globally, fish are the most eaten animal (an estimated 1.1-2.2tn are caught annually ). They are also the most common pet, and one of the main animals used in science and medical research. Yet Brown says most of the public barely even consider them to be animals.

In recent decades, researchers have demonstrated that along with visual self-awareness, certain species have the capacity to learn, remember, experience pain and form relationships. Many of these qualities imply sentience, the capacity to feel positive and negative experiences.

“Science is so far in front of society that it’s going to take a monumental shift in human behaviour to catch up,” he says.

For instance, Brown says the popular misconception that fish have short memories has “absolutely no foundation”. His research on sharks found them to be intelligent and inquisitive creatures with long memories.

He is among a group of scientists and philosophers to sign the New York declaration on animal consciousness earlier this year, which attempts to bridge the gap between science and society. Drawing on evidence, the declaration says there is “at least a realistic possibility of conscious experience in all vertebrates (including reptiles, amphibians, and fishes)”.

The scrutiny of the mirror test led to more studies, including one published this week showing cleaner wrasse will use a mirror to check their size before deciding whether to attack another fish. Fish now have the best supported evidence of any animal for mirror self-recognition, Brown says, yet “people still don’t believe it”.

The implications for scientific experimentation

Pain in fish, an important consideration for animal welfare, is also contested.

Associate professor Nick Ling, a fish ecologist from the University of Waikato, says it’s hard to know whether a fish is experiencing pain “because you can’t ask it”.

But finding out is important, particularly as the use of zebrafish in medical and scientific experiments has “massively increased”, he says.

More than 5m zebrafish are used research annually for studying human diseases, genetics, physiology and drug development.

“You can keep many thousands of them in the lab, very simply and cheaply,” Ling says.

Ling says research into whether fish experience sensations like pain or fear has come a long way in the decades since James Rose, a zoologist, argued fish were incapable of pain given their different brain structure to humans.

Since then, prolific research by Prof Lynne Sneddon at the University of Gothenburg has provided evidence that some bony fish, like the rainbow trout, experience body and behavioural responses consistent with pain. For example, trout injected with bee venom were observed rocking from side to side and increased their gill breathing rate.

Ling says there’s a need for similar studies in other fish. “There are lots of public concerns about how some of these charismatic species, like the big sharks, are treated these days.”

Sharks don’t seem to possess the nerve cells, called nociceptors, that enable the sensation of pain, but that’s no reason to treat them poorly, he says.

‘Consciousness and pain are complex things’

While Ling accepts that some species feel pain, he is cautious about generalising.

“Fish are an incredibly diverse group,” he says. There are thousands of species ranging from huge ocean sunfish to minuscule fish only a few millimetres long.

In biology, concepts like pain and sentience are not binary or straightforward, he says. “These things that we try to understand in other animals, like feelings and emotions and consciousness and pain are really complex things, because the only animal that we know experiences those things is ourselves.”

Psychologist Dr Michael Philipp, from the University of Canterbury in New Zealand, says people’s attitudes towards animal welfare are influenced by their own perceptions of that animal’s capacity to think and feel.

For example, his research shows the acceptability of euthanasia increases for animals that are “delicious to eat”, but decreases for those considered “beautiful”. He says other research shows that when animals are categorised as food or experimental animals , it motivates people to deny the cognitive abilities of those animals.

Countries and regions are beginning to recognise animal sentience, with New Zealand and the ACT extending this to fish.

In New Zealand, experts are raising questions now about the onset of sentience in fish. Most zebrafish used in research are juveniles and specifically excluded from protection under the Animal Welfare Act. But advice from the National Animal Ethics Advisory Committee says there is “persuasive evidence to suggest that fish become sentient well before the transition from larvae to adult”.

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Brown says while arguments around fish sentience, pain and perception might seem complex, the upshot is straightforward. “If they have the capacity to suffer and feel negative things, then we have an obligation to stop that whenever we come across it,” he says.

“You would treat the fish as you would any other animal – a cow, a cat, a dog, or a bird – the same sort of decency and respect for that animal’s life.”

This story was produced with the support of a travel grant from the Science Journalists Association of Australia .