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Intro Bio Psy
Collaborating fish(es)

I stumbled across an interesting paper by Bshary and colleagues about collaboration between fishes1. The study is already a few years old (see a recent follow up). But, new or not, collaborating fishes are always cute and worth writing about.

The fishes in question are the roving coralgrouper and the giant moray. Both are hunters, but their hunting styles differ. The grouper hunts for prey in the open water. To escape from the grouper, fishes tend to hide in the coral reefs, in small crevices where the grouper cannot reach. In contrast, the moray hunts by slithering through the reefs and capturing smaller fishes that hide in the reef’s crevices. To escape from the moray, fishes swim out into the open water. The potential for collaboration is clear: If the grouper and moray would hunt together, there would be nowhere to hide. They would make a deadly team indeed.

And they do hunt together. I tend to be skeptical of claims like this, which (to me) seem extraordinary. But Bshary and colleagues show quite convincingly that some form of collaboration must be going on. It works as follows: When the grouper is hungry, it actively seeks out a nearby moray and shakes its head to signal its intention to hunt. Most of the time, the moray responds by following the grouper. And they’re off–Swimming side by side and hunting. You can see this in the video below:

What I like about Bshary and colleague’s paper is that they don’t make overly strong claims (e.g. ‘amazingly intelligent fishes!’) and don’t anthropomorphize (e.g. ‘deep friendship between fishes!’). Instead, they try to explain how this seemingly complex collaboration can arise between animals that have very limited cognitive abilities. After all, fish are good at many things, but thinking is not one of them.

Part of the explanation may be that the grouper and moray don’t adjust their behavior during collaboration. They don’t exhibit any altruistic behavior, or coordinate the hunt in any other way than by staying close together. They simply do their own thing, as they would when hunting alone–but together. In other words, the grouper and moray don’t need to learn any complex behavior in order to collaborate. They just need to learn to stick together.

Another part of the explanation may be the fact that the grouper and moray swallow their prey whole. This is important, because it avoids conflict. If there would be left-overs, the grouper and moray would almost certainly fight over them–Loyalty between fishes only goes so far. (There I go, anthropomorphizing!) But there are no left-overs to fight over. And therefore, and as long as both fish catch enough prey on average, the collaboration continues.

  1. The plural of ‘fish’ is ‘fish’ or ‘fishes’, but the second is used when referring to different kinds of fish: A goldfish and a salmon make two fishes, but two goldfish make two fish. This semantic distinction between multiple individuals and multiple species is interesting and, as far as I know, unique to fish(es?). Perhaps this is because we don’t see a shoal of fish as a group of individuals, and instead prefer to think of it simply as fish.