The myth that goldfish have only a three-second memory might be giving us an unfair view of their mental capabilities. A new study has shown that some fish can recognize themselves in a photograph, meaning they join a pretty exclusive club of animals known to have some self-awareness.
While it might seem like a basic skill to us, self-recognition is an indication that an animal is capable of higher mental processes. It’s most commonly tested using mirrors – many animals, like dogs, will react to their reflection as though it was another individual, but some are able to recognize that what they’re seeing is themselves. Apes, dolphins, elephants and some birds have passed the test, and it even takes human children about 18 months to figure it out.
A few years ago, a team of scientists investigated whether a fish species called cleaner wrasse could pass the mirror test. They marked the fish with what looked like a parasite on their throats, and placed a mirror in the tank. And sure enough, many of the animals saw the mark in their reflections and rubbed it off their throats, indicating they realized they were looking at themselves. This was confirmed by marking the mirror itself or other fish in adjacent tanks, which didn’t cause the fish to rub off the mark.
In the new study, the researchers took it one step further – they wanted to check whether the fish could recognize themselves in a photograph. They presented each cleaner wrasse with four photos: one of themselves, one of an unfamiliar fish, one with their own face on a different fish’s body, and one with an unfamiliar face on their own body.
Cleaner wrasses are fiercely territorial, and will attack intruders. In this case, they attacked the photos of unfamiliar fish but not photos of themselves. They also didn’t attack the photos of their face on another body, but did attack those of a stranger’s face on their own body, indicating the fish recognize facial features more than bodily ones.
These photo tests show that the fish aren’t just recognizing themselves by matching movements in a mirror – they can actually build a mental model of their own faces. After all, only fish that had been trained on mirrors could pass the photo tests, giving them time to build up these mental images.
A possible alternate explanation was that the fish came to consider photos of themselves as close companions, so to investigate that the team presented them with photos showing a mark on their throats. And sure enough, six out of eight fish shown that image rubbed their throats to clean off the mark, behavior they didn’t display when shown photos of themselves without marks, or photos of other fish with marks.
“This study is the first to demonstrate that fish have an internal sense of self,” said Masanori Kohda, lead researcher on the study. “Since the target animal is a fish, this finding suggests that nearly all social vertebrates also have this higher sense of self.”
The research was published in the journal PNAS.
Source: Osaka Metropolitan University