Fish exchange electrical signals to extend their eyesight

Some fish, it turns out, can “beam” sensory information to other nearby fish to extend their detection range. Working with African electric fish - also known as elephantnose fish, the team, at Columbia University, have found that the animals use electrical receptors on their body to detect external signals as electric images that they then share with among themselves, allowing them to see objects as a group and much farther than they could manage alone. Sannia Farrukh heard from the study lead, Nathaniel Sawtell…

Nathaniel - We built a computer model of the electric fish and its field, and then we could place objects and other fish in different configurations and then look at the electrical images on the skin of the fish. So we could use the model to calculate or visualise how the electrical field of the fish interacts with objects. And we could do this under conditions when the fish was all by itself or when it was in a group. And what we saw from these simulations is that when the fish are in groups, they actually can potentially gain a great deal more information about their environment. And in particular, what we were intrigued by is that in groups, the fish can actually see further away. So an object that would be outside of the range of electro location for the fish when it was on its own, was actually clearly visible to the fish when another nearby fish was also emitting electrical pulses.

Nathaniel - So this idea that came out of this was that the electric fish could amplify their electric sensing in groups. So we saw this first in the model, and then indeed what we were able to see in the brain is that when two fish were nearby each other, we saw electrical signals in the brain of the fish or neural signals in the brain of the fish related not only to the fish's own pulse, but to the pulse of the nearby fish. So when the fish were on their own, we saw this very limited range. But when we added electrical pulses into the water, simulating those from other fish, we saw that the sensing range was dramatically enhanced. So it increased by a factor of two or even factor of three in some cases.

Sannia - I've seen this dubbed as telepathy. Is that a fair comparison or is it more a case of group electric effect? Like how swarms of bees create a much larger electrical charge?

Nathaniel - It's certainly invisible to us. So these electrical fields are emitted by the fish. We can't see them, we can't feel them. They travel at the speed of light. So they certainly have magical qualities, but they're electrical fields, just the same kind of fields, you know, that we deal with when we turn on the light switch. But it is remarkable in that way that the fish are emitting this energy into the water and then the other animals nearby all benefit from that energy. That energy conveys information to the entire group at virtually the same instant.

Sannia - So do you think there could be other species with such abilities?

Nathaniel - In terms of other active sensing animals? The ones that are studied the most are bats and dolphins, both of which use echolocation to sense their environment. Researchers that study those animals have speculated and wondered about these same issues. What happens when bats are in a group or dolphins are in a pod? Are the emissions of the other animals a source of interference or could they help? There's some evidence in those systems that jamming could be a problem. There's a little bit of evidence that the animals could actually sense as a group. So it's something that needs to be investigated more. And we think our studies showing that the electric fish can sense as a group could motivate more studies of these other animals.

Sannia - So what are the next steps of this study? Are you going to look at the neural mechanism?

Nathaniel - We're very interested in the neural mechanism, certainly. And it's, you know, it's worth noting that these fish that we're studying have enormous brains. So they have larger brain to body mass ratios than humans actually. And their brain has evolved in a very interesting peculiar way. The large brains of humans are dominated by the cerebral cortex, which is grown to cover the entire brain in these fish, a different part of the brain. The cerebellum is the dominant part of the brain that covers the entire surface of the brain and makes it so large. So we've often wondered what kind of intelligence these animals have that relies on the cerebellum. In particular, one possibility that this work suggests is that these animals use the cerebellum to make sense of this information that they're receiving in groups. And one thing you could imagine is that in order to sense in a group, you have to have very good knowledge of your group members.

Nathaniel - And you might even need to predict how they're moving in space and keep track of that. And again, since these fish are doing all of this in dark, murky rivers without the benefit of much vision, you'd have to have some pretty sophisticated abilities to be able to keep track of fish in a group. And then all these studies, of course, were done in the laboratory setting and fairly reduced settings. So we were very curious about what are the real ecological functions of this group sensing in the natural habitats of these animals? Do the fish really actively change their behaviour? Do they position themselves in a way that makes this sensing work better? Do they coordinate the timing of their pulses? So the degree of social coordination and cooperation is another fascinating open question that we'll follow up on.