I used to think cleaning stations were just convenient pit stops for fish—like underwater gas stations, basically.
Turns out, they’re way more intricate than that, and honestly, kind of beautiful in a weird evolutionary sense. Cleaner fish—mostly wrasses and gobies, though there are roughly a couple dozen species that do this work—set up shop on coral outcrops or rock formations, and larger marine animals line up for their services. Groupers, manta rays, even sharks will hover there, sometimes for minutes at a time, while these tiny fish pick off parasites, dead skin, and infected tissue. The clients get healthier. The cleaners get fed. It’s mutualism in its most obvious form, except here’s the thing: it’s not always that straightforward. Some cleaner fish cheat. They’ll take bites of healthy mucus or tissue instead of just parasites, which should break the whole system, but it doesn’t. The clients tolerate it, mostly, and researchers are still trying to figure out exactly why.
What’s fascinating is how much communication happens at these stations. Clients will change color, open their mouths wide, spread their gills—basically signaling “I’m not a threat, go ahead.” And the cleaners respond. They’ll dance, almost, doing this little tactile stimulation thing with their fins that seems to calm the clients down. Alexandra Grutter, a marine biologist who’s spent decades studying this, has shown that clients actively choose which cleaning stations to visit based on the reputation of the cleaners there. If a cleaner cheats too much, word gets around—or whatever the fish equivalent of word is—and clients go elsewhere.
The Economics of Not Eating Your Business Partners
One thing I didn’t expect when I first read about this was how much game theory applies. Cleaners have to balance short-term gains (cheating and getting a quick meal of mucus) against long-term benefits (keeping clients happy so they return). And clients have to decide whether to punish cheaters or just tolerate occasional bad service. In some cases, clients will chase or even eat a cleaner that bites too hard, but that’s risky—it destroys the relationship entirely. More often, they just leave and don’t come back, which is a slower punishment but maybe more effective. There’s this whole economic calculation happening, and it’s definately more sophisticated than you’d think for animals without, you know, spreadsheets.
Wait—maybe the most surpising part is that cleaners can recognize individual clients.
Redouan Bshary’s research group in Switzerland has shown that cleaner wrasses can distinguish between different client species and even individual fish within those species, adjusting their behavior accordingly. They’ll prioritize transient clients—fish just passing through—over resident clients who live nearby, because the transients won’t return if they get bad service, while the residents have fewer options and will probably come back anyway. It’s strategic, almost cynical. And the residents seem to know this, because they’ll sometimes leave in the middle of a cleaning session if they see the cleaner prioritizing someone else. The whole dynamic is packed with subtle negotiations and, honestly, a little bit of passive-aggressive behavior that feels weirdly relatable.
When the System Breaks Down (Or Doesn’t, Somehow)
Here’s where it gets messy. Not all cleaning relationships are equally mutualistic. Some cleaners are nearly parasitic—they cheat constantly, and clients still visit them. Why? Partly because in some regions, there aren’t enough cleaners to go around, so clients don’t have a choice. Partly because even a cheating cleaner still removes some parasites, so it’s better than nothing. And partly, I guess, because evolution doesn’t optimize for perfection—it optimizes for “good enough.”
There are also cleaner mimics, like the sabertooth blenny, which looks almost identical to the bluestreak cleaner wrasse but instead of cleaning, it just takes a chunk out of the client and bolts. Clients fall for this trick repeatedly, which seems dumb until you realize that the cost of being overly suspicious—avoiding all cleaners just because some might be mimics—is probably higher than occasionally getting bitten. So they take the risk.
The Broader Implications, Because Everything Connects to Everything
What strikes me most about cleaner fish mutualisms is how much they reveal about cooperation in general. These relationships aren’t held together by contracts or enforcement mechanisms—they’re maintained by reputation, repeated interactions, and the looming threat of defection. Sound familiar? It’s basically how human societies work, just underwater and without the bureaucracy. When cleaning stations get disrupted—say, by overfishing or habitat destruction—the health of entire reef communities declines. Parasite loads on fish increase. Infections spread. The whole ecosystem feels it. And that’s the thing about mutualism: it looks optional from the outside, like a nice bonus, but once it’s established, everything starts depending on it. Remove the cleaners, and you don’t just lose a service—you lose a stabilizing force that was holding a bunch of other relationships together. Anyway, I think that’s worth remembering, even if we’re just talking about fish. Or maybe especially because we’re talking about fish.
