The practice of “cloacal diving” could help remoras hide from predators—it could also be a feeding strategy or help the fish hitchhike
By Jackie Flynn Mogensen edited by Claire Cameron
A remora enters the cloacal opening of a Mobula yarae manta ray in Florida.
Emily Yeager/Ecology and Evolution
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Fish are diving into manta rays’ “butt,” and the rays are perhaps unsurprisingly not thrilled about it, according to new research.
In a new study, researchers documented seven cases of remoras, a fish known for suctioning itself onto rays, as well as sharks, dolphins, boats and even divers, plunging into manta rays' cloacal orifice—an opening used for pooping, peeing and mating. The researchers call the practice “cloacal diving.”
It’s unwelcome behavior, at least on a manta rays’ end. “It does not look like the manta ray likes it,” said Catherine Macdonald, senior study author and a marine biologist at the University of Miami, to the New York Times.
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But for the remoras, shimmying into a manta ray’s behind could offer several benefits, the authors speculate: it could function as a convenient hiding place from predators, a source of food—remoras typically eat a diet made up of their hosts’ feces, scraps and parasites—or simply a hitchhiking spot with “reduced drag,” they write in the study.
Photographs documenting the presence of remoras within manta ray cloacal openings
Remoras have been known to hide in other marine species’ “semi-internal structures,” the study authors write. The fish have been found in the gills and cloacal openings of whale sharks and the mouths of lemon sharks. “However, limited observations of these cryptic behaviors impede scientific descriptions of the mechanisms driving their occurrence,” the researchers add in the study.
It’s unclear how long a remora might stay inside a manta ray’s butthole equivalent. But it’s entirely possible that just a “moderately-sized” remora could “impede mating behavior, live birth, or defecation” if the fish were in there for “extensive periods of time,” the authors write.
The study was published on Monday in the journal Ecology and Evolution.
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