The hidden relationship between manta rays and remoras turns out to include something far stranger than simple hitchhiking. Remoras are the suction-disc fish that ride along sharks, whales, and rays, and for decades biologists assumed the arrangement was harmless, maybe even a small favour, since remoras clean up leftover parasites and scraps. New research shows some remoras are doing something else entirely: diving into a manta ray's cloaca, the single shared opening elasmobranchs use for waste, reproduction, and birth. It isn't a sexual behaviour. Researchers believe the remoras are hiding, most likely from a threat with nowhere else to go in open water, and they come back out once it's safe.
The behaviour is documented in "Hiding in Plain Sight," a study from Emily Yeager and Catherine Macdonald at the University of Miami's Shark Research and Conservation Program, working alongside the Marine Megafauna Foundation and the Manta Trust. The team pieced together seven documented sightings over 15 years, from 2010 to 2025, across three locations spanning two oceans: Florida, Mozambique, and the Maldives. Photographs show remora tails protruding from manta cloacas across multiple individuals and species, and video footage captures the moment it happens: a remora darting toward a manta and disappearing inside within seconds, while the manta visibly reacts to the intrusion. A separate case shows a remora wedged inside a manta's gill slit, alongside mantas with physical injuries researchers say are consistent with this kind of intrusion.
For decades, this relationship was treated as settled and mostly harmless. This study argues that assumption deserves a second look. Whether remoras are hiding from predators, chasing an easy meal, or just resting inside a moving host is still an open question, and so is how much harm, if any, this causes the manta over repeated encounters. What's clear is that this pattern took 15 years of patient, opportunistic observation to surface, a reminder of how much remains unknown about the animals sharing our oceans. If stories like this are your thing, Ocean Decoded Live breaks down ocean news like it every weekday.
Chapters:
0:00 The Mystery: A Manta Ray, a Remora, and a Disappearing Act
1:52 The Moment It Happens: The Remora Vanishes Into the Manta
4:18 Meet the Researchers Behind the Discovery
7:26 Watch: The Remora Diving-In Footage
9:09 Is This Relationship Harmless? Scientists Respond
Takeaways:
Remoras, the suction-disc fish that ride sharks, rays, and whales, have been documented diving inside a manta ray's cloaca, the single shared opening used for waste, reproduction, and birth.
The behaviour is not sexual. Researchers believe remoras use the cloaca, and in at least one case a gill slit, as a hiding spot, most likely from a threat with nowhere else to go in open water.
The study, titled "Hiding in Plain Sight," comes from Emily Yeager and Catherine Macdonald at the University of Miami's Shark Research and Conservation Program, with the Marine Megafauna Foundation and the Manta Trust.
Researchers pieced together seven documented sightings over 15 years (2010 to 2025) across Florida, Mozambique, and the Maldives, plus video footage of a remora diving in.
Scientists had long assumed this relationship was harmless or even mutually beneficial. This study suggests it may sometimes be more intrusive, and possibly harmful, than previously thought.
Whether the behaviour is about hiding from predators, chasing an easy meal, or resting is still unresolved. It's an open question in marine science, not a settled fact.
#OceanConservation #MarineBiology #SaveOurOceans #ProtectTheOcean #OceanAwareness #BluePlanet #ConservationMatters #ScienceForChange #SustainableOceans
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