Sometimes good, sometimes bad, rarely purely one thing
Off the coast of the Atlantic, a diver witnessed a remora fish disappear inside a manta ray's cloaca — a moment small in scale but vast in implication. What science had long classified as a tidy, mutually beneficial arrangement between hitchhiker and host is now being reexamined as something closer to exploitation. Marine biologists are confronting the possibility that the ocean's most familiar partnerships are not fixed agreements but shifting negotiations, shaped by opportunity and power as much as by mutual gain.
- Rare footage of remoras entering manta ray cloacas and gill slits has shaken a foundational assumption of marine biology — that these fish are harmless or helpful companions.
- The intrusion into sensitive reproductive and respiratory openings suggests the relationship may cause real harm: wounds, increased energy drain, and potential interference with breeding.
- Manta rays have been observed leaping from the water and scraping against the seafloor, apparent desperate attempts to dislodge fish that have burrowed inside them.
- Researchers are now arguing that symbiosis is not a fixed category but a spectrum — a relationship that can slide from partnership into parasitism depending on circumstance.
- The scientific community is calling for sustained, close observation of marine interactions, acknowledging that the ocean's social contracts are far more contested than textbooks have suggested.
When a diver watched a remora dart into a manta ray's cloaca and vanish — only its tail still visible — it was the kind of moment that quietly dismantles a long-held certainty. Remoras have always been cast as the ocean's savvy freeloaders: clinging to larger animals, riding currents for free, and earning their keep by picking off parasites and scraps. A harmless arrangement, perhaps even a helpful one. Textbooks sorted it confidently into mutualism or commensalism.
But documented footage of remoras entering not just the outer bodies of manta rays, but their gill slits and cloacal openings — the gateways to breathing and reproduction — has forced marine biologists to look again. Emily Yeager, a researcher at the University of Miami, notes that a remora lodged inside these sensitive cavities can cause injury, force the ray to expend extra energy trying to expel it, and may disrupt reproduction entirely. Manta rays have been seen launching themselves out of the water or grinding against sandy seafloors in what appear to be frantic attempts at relief.
What this footage ultimately reveals is not just a behavioral curiosity but a philosophical one. Yeager argues that symbiotic relationships don't belong in fixed boxes — they exist on a spectrum, capable of shifting between benefit and harm depending on context, scale, and circumstance. She likens them to family: rarely purely one thing. The more closely researchers watch the ocean, the more its apparent partnerships reveal themselves as something messier, more contested, and more alive.
A diver was swimming near an Atlantic manta ray when something unexpected happened. A remora fish—one of those small hitchhikers that cling to larger ocean animals—suddenly darted toward the ray's pelvic fins and, in a moment that would have seemed impossible just moments before, inserted itself directly into the ray's cloaca. Only its tail remained visible. The manta ray shuddered, then continued swimming with the fish still lodged inside.
Remoras have long been understood as the ocean's freeloaders in the best possible sense. These small fish attach themselves to larger marine animals and ride along for thousands of miles, conserving energy that would otherwise be spent swimming. In return, they gain protection from predators and access to an easy food supply: parasites living on their host's skin, leftover scraps from meals, and even feces. It seemed like a straightforward arrangement, the kind of relationship that textbooks classify neatly into categories—mutually beneficial, or at worst, harmless to the host.
But the recent footage, along with other documented observations, has forced marine biologists to reconsider this tidy understanding. Remoras have been spotted not just clinging to the outer bodies of manta rays, but entering their gill slits and cloacal openings—sensitive, essential body parts. In some cases, only the fish's tail remained visible outside the host. The behavior is so unusual that it has prompted researchers to question whether these relationships are actually parasitic rather than symbiotic in the traditional sense.
Emily Yeager, a researcher at the University of Miami's shark research and conservation program, studies these kinds of close, lasting interactions between different ocean species. Traditionally, scientists have sorted symbiotic relationships into three buckets: mutualism, where both animals benefit; commensalism, where one benefits without harming the other; and parasitism, where one organism gains at the expense of its host. The remora-manta ray relationship had always seemed to fit comfortably into the first two categories. Some researchers even suggested that remoras actively helped their hosts by removing parasites.
Yet newer research paints a more complicated picture. The presence of remoras can increase drag during swimming, making movement less efficient and forcing hosts to expend more energy. When remoras are large or numerous, they can actually wound the skin of their hosts. And now, with documented cases of remoras entering the gill slits and cloacas of manta rays—openings critical for breathing and reproduction—the relationship looks less like partnership and more like exploitation. Yeager noted that the suction created by a remora entering these sensitive areas could cause injury, increase the ray's energy expenditure as it tries to dislodge the fish, and potentially interfere with reproduction. Manta rays have been observed jumping out of the water or scraping their bodies against sand in apparent attempts to remove remoras.
What emerges from this research is a more nuanced view of how ocean creatures interact. Yeager argues that symbiotic relationships don't fit neatly into fixed categories but exist along a spectrum, where the balance of benefit and harm between species can shift. She compares these relationships to family bonds—sometimes good, sometimes contentious, rarely purely one thing or another. The more researchers observe the natural world, the more behaviors emerge that challenge our assumptions. Understanding these dynamics, she suggests, is simply a matter of watching closely enough. Each new study, each new observation, reveals another layer of complexity in how marine life actually works.
Citas Notables
The suction can cause wounds or physical discomfort, increase energy expenditure as the ray tries to remove the fish, and potentially interfere with reproduction— Emily Yeager, University of Miami
Symbiotic relationships don't fit neatly into fixed categories but exist along a spectrum, where the balance of benefit and harm between species can shift— Emily Yeager, University of Miami
La Conversación del Hearth Otra perspectiva de la historia
So a remora just swam into a manta ray's cloaca? That seems almost aggressive. Is that what's happening here?
It's more complicated than aggression. The remora was probably startled by the diver and reacted by seeking shelter in the nearest opening. But yes, the fact that it went there—and that researchers have documented this multiple times—suggests the remora is willing to enter spaces that are clearly uncomfortable for the host.
But remoras have been hitching rides on large fish for millions of years. Why would they suddenly start doing this?
They probably weren't suddenly doing it. We just weren't watching the right way. Divers with cameras are a recent addition to the ocean. What looks new is really just newly visible.
Does the manta ray benefit at all from having a remora inside its cloaca?
That's the question researchers are now asking. Traditionally, we assumed remoras cleaned parasites and the host got a free cleaning service. But if a remora is inside your reproductive opening, causing wounds and making you expend energy trying to get it out, the math changes.
So it's parasitism, then. The remora wins, the ray loses.
Not quite. Yeager compares it to family relationships—sometimes good, sometimes bad, usually both. The remora still gets food and protection. The ray still gets some cleaning. But there's also injury, discomfort, and wasted energy. It's not pure parasitism. It's messier than that.
What does this mean for how we understand the ocean?
It means we've been sorting relationships into boxes that don't actually exist in nature. Everything exists on a spectrum. The more we watch, the more we realize how much we've been missing.