The World Fought Against This Scientist. He Won.

Added: 2026-05-12

[00:00:00]In 2019, a Japanese scientist published a paper that would go on to spark a scientific debate lasting more than half a decade. A debate with him on one side and the rest of the world of animal behavior on the other. His name was Professor Masori Koda and he's the first person in the world to provide conclusive evidence that fish are self-aware. Now, you may be familiar with claims over the years of other animals who have passed the mirror test.

[00:00:27]animals like chimpanzees or dolphins who are often thought to be intelligent animals. But Professor Kota's research shows that this behavior can be found in even the most simple animals amongst us.

[00:00:38]But not just that, his findings suggest that how we have tried to assess consciousness for over half a century may be fundamentally wrong. He has spent the last 30 years studying fish and his research on the cleaner rass show that these fish are not only self-aware but possess a level of intelligence that has only been observed in humans so far. Now these are some very big claims and yet even as much of the field pushed back did not let go of the idea. Over the next 5 years he would keep returning with more evidence until one day there seemed to be no other conclusion. To understand why he was willing to challenge one of animal psychologyy's most trusted ideas, we first need to understand who Professor Kota is.

[00:01:28]Kota says his fascination with animals began when he was still a child. He remembers the first time he read a picture book at school called The History of Life, which sparked his curiosity about animals and taught him to really pay attention to the living world around him. Outside of school, he would often go on fishing trips with his father where they would collect the strange and wonderful creatures they found in rivers near his home. That curiosity followed him into university where he began studying animal behavior.

[00:01:55]In class, he found himself fascinated by the diverse species of fish he read about in the African Great Lakes and that eventually led him to conduct his studies near Lake Tanganika.

[00:02:06]There he spent his days living and swimming amongst cichlid fish. And this absolutely captivated him because all the literature had mentioned that fish were primitive creatures who simply operated on instinct. Yet as he swam alongside them, he instead saw a world where individuals recognized one another and lived surprisingly rich social lives. Over the next few decades, Cota devoted himself to understanding just how complex fish really were. And the longer he studied them, the harder it became to believe that fish were as simple and unintelligent as people had assumed. But while Cota was reaching that conclusion through his own work, the scientific world around him was moving in a very different direction.

[00:02:48]Since the first self-recognition studies in chimpanzees, similar claims gradually began to emerge in other animals like dolphins and magpies. These animals were held up as rare exceptions. Species that were intelligent enough to recognize themselves where hundreds of others had failed, and with each new claim, the search seemed to always continue in a familiar direction toward the animals we already imagined as especially intelligent.

[00:03:16]Fish, meanwhile, were almost entirely absent from that conversation. They were far outside the boundaries of what most scientists even imagined as a serious possibility.

[00:03:26]But Kota's experience over the years told him a very different story and eventually he decided to test the question for himself. So next let's take a look together at what he found.

[00:03:43]To answer this question, Koda turned to one of the most famous experiments in all of animal cognition, the mirror test. The logic behind it is quite simple. First, you expose an animal to a mirror for an extended period of time, usually days or weeks. Then, you would place a mark somewhere on its body that can only be seen by using the mirror. In chimpanzees, this is on the forehead, while for cleaner ras, this is on the throat. And then you watch what the animal does. If the animal specifically touches that mark when it looks in the mirror, then it's considered to pass the test. And for decades, this has been the gold standard for how we test for consciousness in animals. So, COD decided to adapt this for cleaner ras.

[00:04:27]For his experiment, he would take the same group of cleaner ras through a sequence of carefully controlled stages.

[00:04:33]He would first expose the ras to a mirror for 2 weeks before putting them through a series of conditions where they had no mark at all, a transparent sham mark, and a visible colored mark with the mirror covered. In the first three conditions, the rass did not exhibit any distinctive behavior that would suggest they could recognize themselves. And in the final condition, the mirror was revealed to the marked fish. And there's a very important detail here. Coded decided to use the color red for the mark as he noticed that the parasites that latch onto them are of a similar color and he felt that this would be an ecologically meaningful mark to the fish. However, there's been no rules around what marks to use for the mirror test over the years and scientists have often used different marks for different animals. Keep this in mind as this is very, very important for what we're about to look at a little bit later. But first, let's take a look at what he found. Keep in mind that Professor Kota lost his vocal cords to lend cancer a few years ago, so his voice may be a little bit hard to hear.

[00:05:55]That's This experiment marked the first time the possibility of consciousness had been observed in fish and cod soon published his findings in a groundbreaking paper in 2019.

[00:06:27]When news of this spread, the scientific community went up in uproar. Many researchers claimed that it wasn't possible or that they simply weren't intelligent enough. There were even people including those who authored the other mirror studies who questioned the results itself saying that the sample size was only four. And this made Koda very angry because many of the earlier mirror studies had relied on similarly small numbers with the original chimpanzeee experiment itself only having a sample size of four. But rather than argue back, he decided to answer the criticism the strongest way he could by expanding the study and testing more fish. And so in a follow-up study, he repeated the process with 14 new fish.

[00:07:11]And in this case, all 14 passed. This brought the total number of cleaner ras tested to 18, the largest sample size of any non-human species tested for mirror self-recognition outside of chimpanzees.

[00:07:26]And not just that, they achieved a much higher success rate compared to most other mirror tests. Now, this is pretty amazing in and of itself, but we aren't done just yet. Because in addition to the 14 new fish, COD also tested two new groups of fish which either had a green or blue mark. These fish would go through the exact same process as those who had the reddish brown mark. And when they were eventually put through the test, their success rate was 0%.

[00:07:54]In that moment, Cota felt a sharp chill run down his spine because if he had instead chosen to do his original experiment with a green or blue mark, he would have arrived at an entirely different conclusion. That cleaner rass weren't self-aware.

[00:08:50]In the following days, the results from this experiment weighed on his mind. He thought about the countless animals that had supposedly failed the mirror test and were deemed as stupid simply because we have been careless about the methodology we used. And the more he thought about the mirror test, the more problems he found. What exactly are they using in the mirror to recognize themselves? It's commonly assumed to be the face, but what if it's something else entirely like the pattern on another body part? Do they actually have a mental representation of themselves much like we do? How long does it take them to recognize their own reflection?

[00:09:26]It turns out no one had done anything to really try and test for these things to Kota. This was unacceptable and that's when he made a decision. If no one had done anything about this process, then he would do it himself. So next, let's take a look together as he tackles each of these issues one at a time.

[00:09:52]The first issue Koda tried to tackle was a way to prove what exactly the fish were using to recognize themselves in the mirror. Over the years, he had repeatedly found that fish seem to identify each other by the patterns on their faces. And that made him think about how humans do something similar.

[00:10:10]See, when we recognize another person, we don't usually begin by looking at their clothes or the rest of their body.

[00:10:15]We look at the face. And that gave Kodo an idea. If cleaner ras were really using the face as the key to identity, then what would happen if you created an image in which the face belonged to one fish while the body belong to another.

[00:10:30]Here is an example of how that looks.

[00:10:32]It's a little bit hard to see at first, but if you pay close attention, you can see that the bottom two images are actually very well photoshopped. And Koda mentioned he was very proud of this. So next, let's take a look at the experiment itself.

[00:10:47]In previous studies, it have been shown that cleaner rats that were shown a mirror for the first time will attack the mirror thinking it's another fish, but will eventually stop when they come to recognize the reflection as themselves. So, when he showed the fish that had already had some time to get used to a mirror the original two images, there were no surprises in the outcome. Next, he would show them the two composite images. If the fish really were looking at their facial features to recognize themselves in the mirror, then they should only attack the image which had the foreign fish's face on it. And when he tested this, that's exactly what he found. But more than that, it also suggests that the fish were able to retain a mental image of themselves from the mirror and then recognize that same image in a photo.

[00:11:52]That night, Cota and his colleagues found themselves in the Yakuniku restaurant, raising a toast to what they had just found. The entire evening carried a quiet buzz of conversation and excitement, and the feeling lingered with them late into the night.

[00:12:08]But the very next day, his inbox was flooded with messages from skeptics all across the world. One of the most frequent arguments was that maybe the fish were not recognizing themselves, but were simply treating the photograph as a close relative, and that's why they didn't attack. Now, Cotto thought this was ridiculous, but rather than wasting time arguing, he decided to push on with the next experiment he had already planned. This time, the cleaner rat would be put through something far more complex than the mirror test, something called the photo recognition test. So, next, let's take a look at this experiment.

[00:12:50]Compared to the mirror test, the photo recognition test has one key difference.

[00:12:55]First, the cleaner ras would go through the same experimental process as the previous mirror test, which gave the fish a chance to familiarize itself with its own reflection. However, instead of having an ecological mark placed directly on their body, this mark would be placed on the photo of that individual. They would then remove the mirror and show the fish their photo with the added mark. If the fish really did retain a mental image of themselves rather than a close relative, then they should attempt to rub the mark of themselves. Now, before we look at the experimental footage, there's two more important details. First, no animal other than humans has ever been able to pass the photo mark test. And second, because photos are 2D, putting a mark on the throat would naturally imply it's on one side of the face. Looking at this photo, it may seem like it's on the left side. However, if you consider this as a mirror reflection, then this would actually imply the mark is on the right side of the face. This was not something KOD initially planned to test for. But this is very important, and keep this in mind as we look at the video itself.

[00:14:01]In this video, you can see that the mirror on the right has been hidden, while on the left, the fish is presented with a photo of itself with a mark near the throat. Pay very close attention to where exactly the fish touches on the sand.

[00:14:17]You can see it consistently rubs the right side of the face. And this is really interesting because fish don't know what photos are and has clearly interpreted the photo as a mirror and is able to orient its actual body with that knowledge. And you can see that it attempts to do this over and over again.

[00:14:35]And with this, the cleaner rat is the only animal that has been shown to be able to pass the photo mark test other than humans. and it provided conclusive evidence that cleaner ras were in fact self-aware and possessed a level of intelligence previously thought only possible by humans.

[00:14:52]That night, Kota and his colleagues found themselves back at the Yakunika restaurant. The past year had been filled with criticism and doubt from voices all around the world. But now, for the first time in a long while, the noise seemed to fade.

[00:15:07]The next day when he returned to work, he found his inbox was flooded again.

[00:15:11]Only this time, the skepticism had given way to recognition.

[00:15:16]Scientists around the world were congratulating him on his work, and people suddenly wanted to hear what he had to say. But despite all this, there was still one question left in Kod's mind. How quickly were they able to recognize themselves in the mirror?

[00:15:36]In the months that followed, Cota would go over the past literature on the mirror test in meticulous detail. He noticed that in all previous experiments, it was assumed that animals would need a very long time to get used to a mirror and were often given several days to a week before any kind of real testing began. But he also noticed a consistent pattern that seemed to occur in all animals that passed the mirror test thus far. First, they'll engage in some form of social action, typically in the form of aggression against their reflection. Then, they start to engage in a series of unusual behaviors known as confirmation behaviors, where they examine their reflections in the mirror.

[00:16:14]Eventually, these behaviors will stop altogether, and it's believed that at this stage, the animal has come to recognize the reflection as itself. So, with all this in mind, there was one final experiment left to run. This time, Kota gave the fish an ecological mark on the throat before they were ever shown a mirror. He then introduced the mirror and paid close attention to their behavior. In particular, he wanted to track exactly when the fish would move through each of the phases and most importantly to identify the moment they first tried to remove the mark from their body, which would serve as definitive evidence that they recognize the reflection as themselves. And before we get into the results, I'd love to hear your guesses in the comments about how long you think they took to recognize themselves. For context, for a 2-year-old child, this process takes about 10 minutes, while people from a community in Papa New Guinea with no prior exposure to mirrors takes around 20 minutes. Now, let's take a look at what Kota found. First, in the initial phase, you can see that the fish engage in what's known as lip fighting, where they repeatedly try to attack their reflection. This is also the same type of behavior that was used to test previous experiments.

[00:17:23]Once this phase finishes, the fish would begin displaying a range of unnatural behaviors. This includes things like swimming upside down, rapidly approaching the mirror, dropping shrimp, which is a type of contingent testing that has also been observed in dolphins where they blow bubbles and other weird behaviors. Over the months that these fish were recorded, these types of behaviors would not be observed consistently at any other time.

[00:17:56]And finally, they would stop their confirmation behaviors and eventually touch the mark on their body. So, how long did all of this take? In a group of just nine fish, the fastest time it took to pass the mark test was just 20 minutes, almost on par with a human, with the average being 82 minutes and the median being 55.

[00:18:18]This was the first time scientists had confirmation of just how quick animals could actually identify the reflection as themselves. Encoded believes self-recognition happens even earlier at the point where confirmation behaviors stop. After all, in humans, that stage is often already taken as evidence that self-recognition has begun, even without a formal mark test. And if that's true, then the real timing becomes even more impressive.

[00:18:53]Foreign speech. Foreign speech. Foreign speech.

[00:19:15]Koda's findings reveal something much deeper than whether one species of fish can pass a mirror test. They challenge a belief that has quietly shaped animal psychology for decades. That self-awareness and perhaps even consciousness belong only to humans and a small group of animals we had already decided were worthy of them.

[00:19:35]For years, we designed experiments in ways that made sense to us. And when other animals failed those tests, we took that failure as proof of an absence of self-awareness, intelligence, and even consciousness itself.

[00:19:48]But Kod's work suggests a more humbling possibility that what we were measuring all these years was not the limits of animal minds, but the limits of our own methods. He believes that to truly understand intelligence and consciousness in other animals, we first need the curiosity and patience to understand their world. And only then can we begin to design experiments.

[00:20:12]And when the animals we study cannot speak to us, then it also requires something else. Imagination.

[00:20:19]The willingness to ask what the world might feel like from inside a life that is not our own. And that is the kind of science COD hopes this research can help move us toward. A science shaped not only by better methodology, but also by humility. A science willing to revisit its deepest assumptions, especially when those assumptions begin to drift too far from what careful observation of nature seems to be telling us.

[00:20:46]When Codo looks out into nature, he sees something far busier and more alive than most of us ever imagine. A world full of creatures solving their own problems in ways we're only beginning to understand.

[00:20:59]And that is precisely why Professor Kota wants to teach us to really appreciate the living world around us, to pay closer attention to forms of life that we have been too quick to dismiss and to remember that if one day we want to understand other minds, then we may first have to learn how to stop looking only for ourselves.