Sh!t Sc!ence

At Sh!t Sc!ence, we argue that all research, no matter how outrageously ridiculous-sounding, has a purpose and contributes to widen our knowledge of the world. Even when it is a study of how fish can be left-handed.

Well… not left-handed, per se. It turns out that a specific type of fish called the scale-eating cichlid has a mouth that is angled a couple degrees. For half these cichlids , the mouth tilts to their left and the for the other half, it tilts to their right.

This particular species could be considered rather foul, leaching off larger fish and ripping off scales from their sides as they obliviously swim. And since this phenomenon was first described in 1993, it was thought that the way their mouth is slanted determines which side of the fish the cichlid will prey on. So we were pretty sure that we knew why, but we weren’t really sure that we were sure.

That is, not until researchers from Toyama University’s Graduate School of Medicine and Pharmaceutical Sciences captured 200 of these fish and ripped them open (they deserve it, let’s be honest). Surprisingly, by analysing the stomach contents of young and adult scale-eating cichlids, it turned out that even though the young fish have slanted mouths, they eat scales from both sides of their prey, and it is only later that they start to attack the fish from the side their mouths lean, when they become more efficient at preying. This tells us that the fish learn how to take advantage of their physiognomy. And this finding makes this curious piece of research important to the field of laterality.

Let me explain. As humans, we love symmetry, and a symmetrical face is a mark of attractiveness. However, our bodies are profoundly asymmetrical. Researchers are very interested in laterality, i.e. why humans and other animals use one side of their body more than the other.

Most humans are right-handed, and it turns out we are mostly right-sided as well, we will prefer to use our right foot, our right eye, our right ear… Why is this laterality so strongly ingrained in our biology? It is thought that in our species, Homo sapiens, our strong laterality is a result of the literal laterality of our brains, our centre for language residing in our left hemisphere, perhaps encouraging us to use our right hand. But we still don’t know whether laterality is genetic or acquired. Studies such as this one, showing an example of behavioural laterality, where the phenomenon is acquired through learning, give us better insights into our own development.