Fish Found to Assess Symbiotic Cleaners Before 'Hiring' Them

In the human world, peeking at your neighbors as they're cleaned is frowned upon, but some fish rely on information gained by rudely spying on their neighbors to survive.

Fish living in coral reefs often pick up skin parasites or experience buildup of dead skin cells.

To keep healthy and tidy, the fish rely on small "cleaner" fish to nibble away the parasites and detritus.

A new study, detailed in the June 22 issue of Nature, reveals that "client" fish choose their cleaners by watching them go to work on other fish.

One common cleaner fish, the yellow-, blue- and black-striped Labroides dimidiatus, or striped cleaner wrasse, which lives in the Indian and western Pacific oceans, can choose to remove parasites from the skin of clients — or it can cheat and dine on the clients' mucus, the tastier option.

But there is no penalty for cheating. The clients, which in this study were all of the species Scolopsis bilineatus, or bridled monocle bream, rarely eat their cleaners, even the cheaters.

So scientists have long wondered why cheating isn't rampant.

It all comes down to the hiring process and how clients "eavesdrop" to select the most trustworthy cleaners.

The researchers set up an experiment where client fish could observe two cleaners — one dutifully munching away at another client's parasites, the other swimming freely near another client.

Taking the cleaner fishes' past performances into account, the clients chose the cooperative, hard-working fish significantly more often than they did the loafers.

The authors suggest that the client fish establish a rating system for the cleaners they observe and enlist the aid of those that score highly.

The finding illustrates that complex social networks exist in the aquatic world and that this type of selective behavior could be the evolutionary roots of altruism and reputation.

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