This Fish Hitches Rides in Manta Rays’ ‘Buttholes,’ According to New Research

Scientists suspect that the behavior could harm the manta rays, suggesting a complex relationship between remoras and their hosts that can sometimes be parasitic

May 14, 2026 3:56 p.m.

Fish tail sticking out of an opening under a manta ray — Remoras might dive into manta rays' rear ends when they're scared. Bryant Turffs / Marine Megafauna Foundation

Remoras are often called “suckerfish” because of the suction cup-like organ atop their heads. It allows them to stick onto marine animals like whales, rays and dolphins so they can travel as hitchhikers. But it turns out that these clingy fish aren’t just attaching themselves to their hosts’ exteriors.

Sometimes they take a deep dive where the sun doesn’t shine.

In a study published May 11 in the journal Ecology and Evolution, researchers describe several instances of remoras burrowing deep inside manta rays’ backsides. The behavior, called “cloacal diving,” further hints that the relationship between the two types of animal is more complicated than previously thought.

“My first reaction was a combination of amazement and horror—it’s so cool that remoras can do that, but I imagine it’s no fun for the manta,” David Shiffman, an independent marine conservation biologist and author based in Washington, D.C., who was not involved with the study, tells Live Science’s Bethany Augliere.

Remoras are a group of eight fish species that belong to the Echeneidae family. They can range in length from about 12 inches to 43 inches. The long, slender fish are known to catch rides with manta rays, huge animals that can have a wingspan up to 26 feet.

Researchers have debated the nature of remoras’ relationships with their hosts. In some instances, both the remora and the host benefit, since the suckerfish eats parasites on the animal. Other times, a remora profits by getting a trip, while the host reaps neither benefit nor harm.

However, evidence is building that a suckerfish may sometimes hurt its host, since its attachment can cause physical injury and increase drag as the host swims. What’s more, remoras have occasionally been spotted entering semi-internal structures, like a whale shark’s cloaca—an opening for waste excretion and reproduction.

Fun fact: Cloacae are common

In addition to certain cartilaginous fish, many other animals—including amphibians, reptiles, birds and egg-laying mammals, i.e., platypuses and echidnas—have cloacae. The word comes from Latin for “sewer.”

To further investigate, researchers looked at survey data collected between 2010 and 2025 by the Marine Megafauna Foundation and the Manta Trust at known manta ray aggregation sites, including those near Florida, the Maldives and Mozambique. Analysis revealed seven observations of cloacal diving across all three known manta ray species.

“The remoras are pretty much as wide as the cloaca is,” says study co-author Emily Yeager, a marine ecologist at the University of Miami, New York Times’ Jason Bittel. “So it’s fully filling that opening.”

The documented behaviors took place in multiple ocean basins and show that large remoras can dive into both juvenile and adult manta rays. Some pictures in the study capture just the remora’s tail peeking out of the host’s opening. Additionally, Yeager and her colleagues identified one instance of a suckerfish beneath a host’s gill slit, and several observations of gill injuries probably linked to the freeloaders.

tip of a fish's tail barely sticking out of a manta ray's cloacal opening — Sometimes, the fish could barely be seen hiding in the cloacal opening. Jessica Pate / Marine Megafauna Foundation

Why are the slender fish taking refuge in the cloaca? Yeager suspects they’re hiding out of fear. In one analyzed video, for instance, a diver swims behind a manta ray and seems to startle a nearby suckerfish, she tells Nil Kӧksal at CBC’s “As It Happens.”

“That remora jumps straight into the manta ray’s cloaca opening,” Yeager says. “That manta ray then shudders pretty violently before continuing on its way.”

And while the researchers can’t exactly ask manta rays how they feel about the intrusion, they think it’s probably uncomfortable for the animals. It might even be harmful, pointing to a sometimes-parasitic relationship with suckerfish.

Brooke Flammang, a biologist at the New Jersey Institute of Technology who also wasn’t involved in the study, tells CBC’s Sheena Goodyear that there is past evidence of remoras’ built-in suction cups damaging their hosts’ skin.

“If they do that in the cloaca opening, which is likely much more sensitive than other parts of the manta ray’s body, it could cause really severe damage and influence reproduction and also excretion of waste over time,” she says.

You Might Also Like

Get the latest stories in your inbox every weekday.