The Cleaner Wrasse: A Fish That Makes Other Fish Smarter - The Atlantic - 0 views
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At particular sites, an itchy individual can attract the attention of the bluestreak cleaner wrasse—a slender fish, with blue and yellow markings and a prominent black stripe. On seeing these colors, the itchy “client” strikes a specific pose, allowing the wrasse to snake across its body, mouth, and gills, picking off parasites and dead skin along the way. The wrasse gets a meal. The client gets exfoliated. A single wrasse works for around four hours a day, and in that time, it can inspect more than 2,000 clients.
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The wrasse are remarkably savvy about how they perform their services. Redouan Bshary, from the University of Neuchâtel, has shown that they sometimes cheat their clients by taking illicit bites of the protective mucus covering their skin. If the clients are watching, the wrasse restrain themselves from such shenanigans, in an effort to maintain their reputation. If disgruntled clients chase them, they try to make amends by offering a complementary fin massage. If high-status clients pop by—large, visiting predators like sharks or groupers—the cleaners prioritize them over smaller fish that live in the area. They’re surprisingly intelligent for fish.
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she captured damselfish from various reefs and put them through a series of challenges. First, she put square plates on either side of their tank. One of these hid a chunk of food that the fish could smell but not reach, while the other hid a more accessible morsel. The damselfish had to learn which plate to swim up to—a simple spatial-memory test, and one that every individual passed. Next, Binning swapped the location of the correct plate; again, all the fish learned to change their behavior.
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hings changed when she gave them a more difficult task. This time, they had to approach the correct plate based not on its location, but on its appearance. This skill—visual discrimination—is vitally important to a damselfish. “They have to learn very quickly, on the basis of color and pattern, which fish are safe to be around, and what competitors or friends look like,” says Binning. “They’re very good at that.”
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Without the cleaners, the damselfish might also not have enough energy to fully fuel their demanding brains. They’re targeted by parasitic, bloodsucking crustaceans, which makes them “anemic, sluggish, and weak,” Binning says. When cleaners remove these parasites, the distressed damsels can divert their energies toward other matters—like thinking.