Ocean sunfish earned the label “useless” not from any scientific assessment but from a profanity-laced internet rant that went viral around 2017, portraying the fish as a blundering evolutionary mistake that can barely swim, eats nothing but jellyfish, and has no business being alive. The post was funny, widely shared, and almost entirely wrong. Peer-reviewed research paints the ocean sunfish as a surprisingly sophisticated animal with active hunting behavior, efficient locomotion, and a body plan refined over roughly 68 million years of evolution.
Where the “Useless” Reputation Comes From
The meme originated as a Facebook and Reddit copypasta that mocked the sunfish for a long list of supposed failures: it has no real tail, it floats around aimlessly, it can only eat jellyfish, it gets riddled with parasites, it has a tiny brain, and its only survival strategy is producing an absurd number of eggs to compensate for its inadequacy. The rant was entertaining precisely because it sounded plausible to anyone who had ever seen a sunfish drifting at the surface like a dinner plate someone forgot to throw away. It tapped into a real human instinct to judge animals by mammalian standards of speed, agility, and visible intelligence. But judging a deep-ocean fish by those criteria is roughly as fair as judging a cheetah by its ability to hold its breath underwater.
Several of the rant’s specific claims were factually incorrect, and others took real traits wildly out of context. The rest of this article walks through the major accusations and what the science actually shows.
The Missing Tail That Is Not Actually Missing
The most visually striking thing about a sunfish is that it appears to have no tail. Its body looks like the front half of a normal fish that somebody cut off behind the dorsal and anal fins. This is the feature that invites the most ridicule, and it is also one of the most interesting things about the animal.
Sunfish do lack a true caudal fin. During development, the tail fin never forms. Instead, the rear edges of the dorsal and anal fins grow toward each other and fuse into a broad, stiff structure called the clavus. Developmental studies have confirmed that the rays making up the clavus are identical in composition to regular dorsal and anal fin elements and form by closing inward from both fins.1PubMed. Leis’ conundrum: homology of the clavus of the ocean sunfishes. Ontogeny of the median fins and axial skeleton of Ranzania laevis (Teleostei, Tetraodontiformes, Molidae) The spinal column itself never flexes upward during development the way it does in most bony fish, meaning the caudal fin is not degenerated or broken off but genuinely absent from the body plan.
This is not a defect. It is a derived trait, meaning it evolved from an ancestor that did have a tail, and was retained because it works. The clavus serves as a rudder and contributes to the animal’s unusual swimming style, which turns out to be far more capable than it looks.
How Sunfish Actually Swim
The viral rant portrayed sunfish as hopeless swimmers, barely able to control where they go. Biomechanical research tells a very different story. Sunfish swim by stroking their tall dorsal and anal fins synchronously from side to side, generating lift-based thrust in the same fundamental way that penguins use their flippers. Accelerometer data showed that each stroke, whether left-to-right or right-to-left, produced forward thrust, with both fins beating at a frequency of about 0.3 to 0.6 strokes per second.2PLoS ONE. Functional Dorsoventral Symmetry in Relation to Lift-Based Swimming in the Ocean Sunfish Mola mola
This is not thrashing around randomly. It is a coordinated, symmetrical propulsion system that exploits the sunfish’s unusual body shape. The dorsal and anal fins are positioned nearly opposite each other, giving the animal a functional dorsoventral symmetry that lets it generate thrust efficiently in open water. Sunfish are not built for burst speed or tight maneuvering around coral reefs, but they are built for sustained cruising across vast stretches of open ocean, which is exactly what they do.
Deep Divers, Not Lazy Surface Drifters
One of the most persistent images of the sunfish is a big flat disc floating motionless at the surface, seemingly doing nothing. That surface behavior is real, but characterizing it as laziness misses the point entirely. Tagging studies have revealed that sunfish are active deep divers that routinely descend to 100 to 200 meters during the day to hunt in cold water, then return to the surface to warm back up.
Their body temperature drops during these deep foraging dives into water below 12°C, and the subsequent time at the surface functions as thermoregulation, allowing the fish to recover body heat from the warmer water near the surface.3PubMed. Ocean sunfish rewarm at the surface after deep excursions to forage for siphonophores More recent work suggests sunfish can actively alter their rate of heat exchange between warming and cooling phases, losing heat more slowly during deep cold dives and gaining it back more quickly at the surface.4Journal of Experimental Marine Biology and Ecology. Thermoregulation of ocean sunfish in a warmer sea suggests their ability to prevent heat loss in deep, cold foraging grounds That is a form of physiological thermoregulation, a trait shared with some tunas and sharks but not exactly what you expect from an animal dismissed as brainless.
So when you see a sunfish lying on its side at the surface, it is not napping or lost. It is recharging after a hunting trip to depths that would chill most fish into sluggishness.
The Jellyfish Diet Myth
The claim that sunfish eat “only jellyfish” is one of the rant’s most repeated lines, and it is also one of the easiest to debunk. While gelatinous zooplankton, particularly siphonophores, do make up a substantial part of the ocean sunfish diet, molecular and observational studies in the western Mediterranean have found significant contributions from arthropods, mollusks, and chordates as well.5Reviews in Fish Biology and Fisheries. Unravelling the trophic ecology of the ocean sunfish Mola mola in the western Mediterranean Sea through integrated approaches This makes the sunfish a generalist feeder, not a specialist locked into a single low-calorie food source.
The siphonophore preference is itself more interesting than it sounds. Siphonophores are colonial organisms that can stretch meters long, and hunting them at depth in cold, dark water requires the active diving behavior described above. These are not animals washing passively into a sunfish’s mouth at the surface. The fish is going after them deliberately, at significant metabolic cost, hundreds of meters below where most people ever see a sunfish.
The Tiny Brain Question
Sunfish do have small brains relative to their body size. Medical imaging studies have confirmed that ocean sunfish possess very reduced brain and spinal cord structures.6PubMed. Visceral anatomy of ocean sunfish (Mola mola (L., 1758), Molidae, Tetraodontiformes) and angler (Lophius piscatorius (L., 1758), Lophiidae, Lophiiformes) investigated by non-invasive imaging techniques The spinal cord is particularly unusual: in sunfish and their relatives, it tapers to a thin filament almost immediately after leaving the skull.7PubMed. The shortened spinal cord in tetraodontiform fishes
But brain size is a poor proxy for behavioral competence in fish. Many fish with small brains relative to body mass navigate complex environments, learn from experience, and carry out sophisticated behaviors. Sunfish clearly manage coordinated swimming, active foraging at depth, thermoregulatory cycling between deep and surface water, and interactions with cleaner organisms. Whether they are “smart” in any human-relatable sense is beside the point. They are competent enough to survive across most of the world’s temperate and tropical oceans, which is a reasonable definition of adequacy.
Parasites and the Basking Behavior
The rant made much of the fact that sunfish are covered in parasites, as if this were a sign of failure. In reality, heavy parasite loads are common across many large marine animals, and sunfish have developed behavioral strategies to deal with them. Observations in the North Pacific documented a school of 57 ocean sunfish heavily infested with Pennella parasites around the base of their dorsal fins. Researchers photographed a Laysan albatross picking parasites off one of the fish and eating them, suggesting a symbiotic cleaning relationship.8PubMed Central. Why does the ocean sunfish bask?
This finding reframes the basking behavior yet again. Beyond thermoregulation, sunfish at the surface may be presenting themselves to seabirds and other cleaners for parasite removal. Photographs from the same study showed extensive scarring where parasites had been removed, indicating the cleaning relationships are not one-off events but a regular part of sunfish biology. Recruiting other species to manage your parasite burden is not a sign of helplessness; it is an ecological strategy that works, as anyone familiar with cleaner fish on coral reefs would recognize.
The Egg Strategy
Perhaps the single most mocked fact about sunfish is their reproductive output. A female ocean sunfish can produce an enormous number of eggs, with estimates running into the hundreds of millions per spawning event. This is sometimes framed in the rant as the fish’s only survival trick: sheer desperation breeding to compensate for a body that cannot do anything else right.
In reality, high fecundity is standard among broadcast-spawning ocean fish and has nothing to do with individual incompetence. The sunfish sits at the extreme end of a spectrum that includes many successful ocean species.9Journal of Fish Biology. Fish Ecology The strategy works because pelagic eggs and larvae face enormous predation and environmental mortality. Producing vast numbers of offspring is the evolutionary solution to an environment where any individual egg has an infinitesimal chance of surviving to adulthood. Calling this strategy “useless” is like calling dandelions failures because they produce thousands of seeds instead of growing armor.
Five Species, Not Just One Awkward Fish
Part of the public’s confusion about sunfish comes from treating them as a single weird species. The family Molidae actually contains five recognized species across three genera: Mola mola, Mola alexandrini, Mola tecta (only formally described in 2017), Masturus lanceolatus, and Ranzania laevis.10Marine Policy. The ocean sunfishes (family Molidea): Recommendations from the IUCN molidae review panel These species vary considerably in size, shape, and habitat use. Mola alexandrini appears to be the true giant of the family, with specimens exceeding the commonly cited records for Mola mola. Ranzania laevis, the slender sunfish, looks almost nothing like the dinner-plate shape most people picture.
Genomic analysis places the split between sunfish and their closest relatives, the pufferfishes, at roughly 68 million years ago.11PubMed Central. The genome of the largest bony fish, ocean sunfish (Mola mola), provides insights into its fast growth rate That is a long time for evolution to have weeded out a body plan that does not work. Lineages that are genuinely maladapted do not persist for tens of millions of years across multiple species.
Predators That Take Sunfish Seriously
If sunfish were truly useless lumps of tissue drifting through the ocean, predators would barely register them. In fact, orcas actively hunt them. Researchers documented 21 predatory interactions between orcas and sunfish in the Gulf of California between 2013 and 2024, involving three different sunfish species.12Regional Studies in Marine Science. Orca and ocean sunfish: Predator-prey interactions and sightings in the Gulf of California, Mexico Orcas are selective predators that invest energy in hunts proportional to the caloric payoff. The fact that they target sunfish repeatedly suggests the fish represent a worthwhile meal, which in turn means sunfish contain enough energy to be worth chasing down, not exactly the profile of an animal with “no nutritional value” as the meme claims.
Sea lions, large sharks, and other marine predators have also been observed feeding on sunfish. The animals are part of real food webs, transferring energy from the deep gelatinous organisms they eat to the apex predators that eat them.
Real Threats to Sunfish
Ironically, while the internet debates whether sunfish deserve to exist, the animals face genuine conservation concerns that have nothing to do with their own biology. Sunfish are frequently caught as bycatch in commercial fishing operations. Their slow-moving surface behavior and large body size make them easy to accidentally net or hook. Along coastlines like the Egyptian Mediterranean, fishing activity is identified as the major threat to sunfish populations, compounded by the ingestion of macroplastics that the fish apparently mistake for their gelatinous prey.13IntechOpen. Vulnerable Marine Vertebrates along the Egyptian Mediterranean Coast: Challenges to the Anthropogenic, Fisheries Bycatch and Climatic Changes
The IUCN has assessed various sunfish species with differing conservation statuses, but the overall picture is one of increasing pressure from human activity. Animals that survived 68 million years of natural selection are now contending with longlines, drift nets, and floating plastic bags that look like siphonophores.
Sunfish as Tourism Assets
If further proof were needed that sunfish are not worthless, consider that they drive significant economic activity. The waters around Nusa Penida in Bali, Indonesia, attract over 200,000 tourists per year, with ocean sunfish and manta rays among the headline attractions that draw divers to the area’s 20 dive spots.14Transylvanian Review of Systematical and Ecological Research. Nusa Penida Marine Protected Area (Mpa) Bali – Indonesia: Why Need to be Protected? Sunfish appear seasonally in these waters, and their predictable visits have become a cornerstone of local marine tourism.15Jurnal Biologi Tropis. Sunfish’s (Mola spp.) Habitat Characteristics on their Appearance at Dive Tourism Depths in Nusa Penida Waters, Bali
Similar dive tourism operations exist in Portugal, South Africa, Japan, and parts of California, wherever sunfish appear reliably enough for operators to build schedules around them. An animal that people will fly across the world to see underwater is performing an economic function that plenty of “useful” species cannot claim. The ecotourism value also creates a financial incentive for marine protection in regions where sunfish occur, linking the animal’s survival to the livelihoods of coastal communities.
Why the Meme Stuck
The “useless sunfish” narrative endures because it scratches a very human itch. We enjoy the idea that nature sometimes makes mistakes, that evolution can produce something laughably bad. It is the same impulse behind jokes about pandas being too lazy to reproduce or koalas being too dim to recognize their own food. In each case, the comedy depends on applying human values to an organism that evolved under completely different pressures.
Sunfish look alien. They lack the streamlined torpedo shape we associate with competent ocean fish. They float at the surface in a way that seems purposeless. They get covered in parasites. Their body proportions seem wrong. All of this makes them easy to mock, especially in a short, punchy social media post that does not pause to ask why any of these traits might have persisted for millions of years. The rant was comedy, not science, and it was never meant to be taken literally. The problem is that enough people did take it at face value that it shifted public perception of a genuinely remarkable animal.