Hawaiian cleaner wrasse, Labroides phthirophagus. The hard-to-pronounce species name comes from PHTHIRO, Greek for louse, and PHAGUS Greek for eat. © Photo courtesy Russell Gibert
October 2, 2021
Years ago, as a novice snorkeler and diver, I loved watching Hawaii’s 4-inch-long endemic cleaner wrasses nibble parasites off other fish. What a great service, I thought, watching fish customers hold still, and sometimes even line up, for their turn at the spa. Too bad fish in other parts of the world don’t get such treatment.
They do, I later learned. Although the Hawaiian cleaner wrasse is found only in Hawaii, four of its close cousins are found throughout the warm waters of the Indian and Pacific Oceans. All species are similar in size with each sporting its own color patterns. Common names are: bluestreak, blackspot, bicolor, red lip, and Hawaiian cleaner wrasse.
A bluestripe cleaner wrasse tickled my leg during a snorkeling excursion in Tahiti. Finding no parasites on this sailor’s hairy leg, the little fish soon left. ©Susan Scott
Like their invertebrate coworkers, the banded shrimp (my previous post on September 6th), cleaner wrasses make their living by picking parasites, dead skin, and mucus off fish or any other creature that holds still for it.
My cleaner wrasse pair set up shop near a turtle cleaning station, where fish scour algae and parasites off the turtles’ shells and limbs. The wrasses often join in. © Susan Scott
© Susan Scott
Hawaii’s brightly-colored wrasses often work in twos or threes, setting up business in one area and staying there. Wrasse cleaning stations attract fish that need pests or injured flesh removed, but sometimes, the clients just want a massage. As the cleaners work, their fins rub against the client’s skin. This apparently feels good, because fish with no parasites also show up, and hold still while the wrasses work them over.
Three fish — a saddle wrasse (foreground), a goldring surgeonfish, and a yellow tang — wait for service at this cleaner wrasse station. ©Susan Scott
Cleaner wrasses prefer eating mucus secreted by their clients more than crustacean parasites. Fish skin mucus consists of protein and carbs, a nutritious mixture with antibiotic qualities that have potential in treating human infections. Here, my pair of cleaners work over a pufferfish. ©Susan Scott
Sometimes, cleaners get rough with their clients, biting into healthy flesh or gobbling up too much of the fish’s essential mucus.
If a wrasse bites its client, such as this manybar goatfish, or moana, the fish darts away, and returns later. In this way, the wrasse learns the fine line between too timid or too aggressive in eating the fish’s mucus and skin. © Photo courtesy Russell Gilbert
Because parasites and mucus are abundant inside fishes’ gill covers, reef fish allow cleaner wrasses to delve deep. This is a whitesaddle goatifsh, or kūmū. ©Photo courtesy Russell Gilbert
To determine what kind of food cleaners preferred, researchers trained captured bluestreak cleaner wrasses to eat off plates (a charming image) each containing a different offering. The wrasses preferred mucus to parasites.
This suggests that cleaner wrasses remove parasites in exchange for sips of mucus. This kind of partnership is called mutualism.
Mutualism at its most striking. This looks like a death wish for the little wrasse, but even fish-eating predators such as this white-mouth moray eel, allow cleaner wrasses to do their work unharmed. © Courtesy David Schrichte
In one Australia study of bluestreak cleaner wrasses, researchers found that the cleaners averaged 4 hours per day inspecting over 2,000 fish, during which they found and ate about 1,200 tiny crustacean parasites. This reduced the number of pests on the fish by about 50 percent, but it didn’t last long. In 1-to-6 days, the parasite load on a cleaned fish was back to 100 percent. In the ocean as well as on land, the work of cleaning is never done.