We humans like to think we’re special creatures. We have rich emotional landscapes that are far more complex than those of, say, fish. Right?

A recent study shows that fish are more emotionally complex than we give them credit for. Scientists at the University of Burgundy in France studied one called the convict cichlid, a monogamous fish species that forms long-lasting pairs. They found that when female cichlids lose their chosen mates, they become glum and more pessimistic about the world.

It turns out emotional attachment to a partner is not unique to humans or even to mammals. Breakups really suck, even if you’re a fish.

The scientists started by giving females a chance to express a preference between two males. In a tank partitioned into three compartments, the female fish was put in the middle, and a male was put on either side of her. After seeing, hearing, and — let’s be real — judging them through the mesh partitions, she huddled up close to the one she liked best.

But the scientists didn’t allow all the female fish to stay with their chosen mates. In some cases, the researchers split them up and paired the females with the males they’d rejected. They found that these unfortunately paired fish couples were slower to spawn than the others.

Now, the scientists switched gears. They exposed the female fish to little clay boxes in the tank. Boxes with white lids contained food (one yummy larva, to be exact), while boxes with black lids contained nothing. The fish learned that with some effort, they could suck or push off the lids, and they gradually figured out that a white lid means there’ll be a treat inside.

Here’s the tricky bit: The scientists then introduced a third kind of box, this one with a grey lid. They wanted to see how the female fish would respond to an ambiguous signal — halfway between white and black — and whether the response would correlate with whether the fish had gotten to stay with her chosen mate or had been separated from him and paired with the reject instead.

The researchers hypothesized that females who’d been made optimistic by a positive experience would push off the grey lids, expecting to find food, while females who’d been made pessimistic wouldn’t bother to make the effort.

And that’s exactly what happened. “Females that were assigned their non-preferred partner exhibited pessimistic bias,” the researchers wrote in the journal Proceedings of the Royal Society B, “which indicates a negative affective state.”

Or as Chloé Laubu, the study’s lead author, explained, “A good analogy would be the way you perceive the glass either half-full or half-empty according to your mood.”

Studies like these are important because they can challenge our conventional views of which animals possess sentience — the ability to feel sensations like pain and pleasure — and to what degree. Psychologists have found that when we attribute a higher degree of sentience to an animal, we’re more likely to include it in our moral circle, the imaginary boundary we draw around those we consider worthy of ethical consideration. So if we start to see fish as creatures that feel emotional pain akin to ours, it could change how we treat them.

How we assess an animal’s level of cognitive complexity

Experiments like the one performed by the University of Burgundy researchers are known as judgment bias tasks, and they’ve been used to assess the emotional states of other animals, particularly mammals and birds. Finding out what causes an animal to display pessimistic bias is an important part of animal welfare research. A 2015 review of 64 animal studies noted that judgment bias tasks “can provide new insight into welfare in endangered species housed in zoos and aquariums, where poor welfare impacts breeding success and, ultimately, species survival.”

The University of Burgundy researchers say their study marks the first time a judgment bias task has been used to demonstrate the emotional attachments of fish to their partners. This study stands to change our perception of fish as being much less complex creatures than we are, especially when we combine it with a study published in PLOS Biology in February suggesting that fish can pass the “mirror test” — the classic test that scientists use to determine if a species is self-aware.

In that study, scientists observed a striped species of fish known as the cleaner wrasse. They placed a colored mark on the fish’s throat, which it would only be able to see in its reflection. They noticed that the fish used the mirror to check out the mark and then tried to remove the mark by scraping its body. It appeared to recognize itself, thus passing the test for self-awareness.

Some researchers disputed that result. Previously, the only animals who’d passed the test were great apes, bottlenose dolphins, European magpies, and one Asian elephant (and even some of those results were disputed). These researchers were reluctant to believe that fish, which are often viewed as cognitively vacant, could enter the esteemed ranks of such species.

“When it’s a fucking elephant and one of two elephants passes the test, everyone’s like ‘Yeah cool,’” said Alex Jordan, one of the study’s authors. “When it’s a fish they’re like, ‘Ooh you need a conspecific control and a control for empathy and a control for this and that … the fish are not doing this.’”

Jordan suggested that people may doubt these results partly because fish look so different from us, and partly because recognizing their cognitive complexity would force us to change our lifestyles, including “our entire practice of commercial fishing [that] lets these animals die in stress and pain.”

In other words, maybe we’re the ones doing something fishy.

Watch: The right way to kill a fish

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