A ray is a flat-bodied fish with a cartilaginous skeleton, belonging to the superorder Batoidea, a group that includes stingrays, manta rays, electric rays, skates, and sawfishes. There are over 600 known species, and they live in oceans worldwide as well as some freshwater rivers. What sets them apart from their close relatives the sharks is a dramatically flattened body with enlarged, wing-like pectoral fins fused to the head, gill slits on the underside, and eyes perched on top. Their diversity runs from tiny electric rays barely a foot across to giant oceanic mantas spanning seven meters, and the group has evolved feeding strategies, defenses, and body shapes that are far more varied than most people realize.
How a Ray’s Body Is Built
Rays share with sharks the distinction of having skeletons made entirely of cartilage rather than bone. That keeps their bodies remarkably lightweight relative to their size, which is part of what allows them to support those broad, flat pectoral “wings.” At the structural level, each pectoral fin is made up of thin, radially oriented fin rays, which are chains of small mineralized cartilage elements stacked end to end like beads on a string. These elements, called tesserae, tile the surface of the cartilage to give it stiffness where needed while remaining far lighter than bone would be.1PubMed. Structure and mechanical implications of the pectoral fin skeleton in the Longnose Skate (Chondrichthyes, Batoidea)
The flattened disk shape that people associate with rays actually evolved more than once. Skates and stingrays share a rounded pectoral disk that stretches all the way to the tip of the snout, supported by fin radials, but studies of their evolutionary relationships indicate that these two groups arrived at that shape independently rather than inheriting it from a single ancestor.2PubMed Central. Body plan convergence in the evolution of skates and rays (Chondrichthyes: Batoidea) The same kind of convergence shows up in sawfishes, whose long, tooth-studded snouts look strikingly similar to those of sawsharks, which are not batoids at all. Evolution, it seems, keeps rediscovering the same body-plan solutions for life on or near the seafloor.
Two Ways to Fly Underwater
If you have watched footage of a stingray and a manta ray side by side, you may have noticed they move in completely different ways. Stingrays send a wave rippling down the length of their pectoral fins, much like a ribbon fluttering in the wind. Mantas and their relatives, by contrast, flap their fins up and down in broad, powerful strokes, more like a bird in flight. Scientists categorize these as rajiform (undulatory) and mobuliform (oscillatory) swimming, respectively, and the two styles are reflected in measurably different body shapes.
Rays that use the wave-like undulatory mode tend to have circular or diamond-shaped outlines with a low aspect ratio, meaning their fins are wide relative to their length. Their bodies are also thicker in cross-section and more cambered, a shape that helps reduce drag when cruising along the bottom. Oscillatory rays like mantas, on the other hand, have high aspect ratio fins resembling the long, tapered wings of an albatross, with a more symmetrical, airfoil-like cross-section suited to generating lift and thrust from flapping.3Journal of Experimental Marine Biology and Ecology. Two- and three-dimensional geometries of batoids in relation to locomotor mode The fin shape essentially tells you how the animal makes its living: bottom-dwelling species favor the undulatory approach, while open-ocean species favor flapping flight.
What Rays Eat and How They Get It
Most rays are predators of small bottom-dwelling animals. Stingrays and skates root through sand and mud for clams, crabs, worms, and shrimp, using their flat bodies to pin prey against the substrate and crushing hard shells with rows of plate-like teeth. Some species have jaws powerful enough to crack open thick-shelled mollusks with ease. But the dietary range across the group is enormous.
At the other end of the spectrum, manta rays and their smaller cousins the devil rays are filter feeders that consume vast quantities of zooplankton. Their feeding apparatus is unlike that of any other filter-feeding fish. Most filter feeders use elongated gill rakers to sieve food from water, but mobulid rays have evolved highly modified, flattened, lobe-like filter structures on their gill arches. Some of these lobes are smooth, while others are covered in tiny cilia or denticles.4PubMed. The filter pads and filtration mechanisms of the devil rays: Variation at macro and microscopic scales Water entering the mouth must make an abrupt ninety-degree turn before passing through the lateral filter pores, across the gill tissue, and out the gill slits on the underside of the body. That sudden change in flow direction creates a shearing force across the filter surface, which helps keep food particles from clogging the filter.
Research on manta ray feeding has revealed something even stranger. Rather than simply trapping plankton in a mesh like a coffee filter, mantas use what has been described as “ricochet separation.” Tiny particles that hit the wing-like filter structures bounce away from the pores instead of plugging them, allowing the filter to handle high flow rates without clogging. This mechanism can separate particles that are actually smaller than the pore openings, which is not something a simple sieve can do.5PubMed Central. Manta rays feed using ricochet separation, a novel nonclogging filtration mechanism Engineers have taken notice; the design principles could inspire new industrial filtration systems.
Stingers, Venom, and Electric Shocks
Rays are not aggressive animals, but several groups carry impressive defensive hardware. The stingray’s tail spine is the most familiar example. A barbed stinger sits on the tail, connected to a venom gland and wrapped in a thin sheath of tissue. When the tail strikes a threat, the stinger and its sheath can break off and become embedded in the wound, and venom is delivered directly into the tissue. The result is intense, sometimes excruciating pain, though the precise mechanism by which the venom produces pain is still not fully understood.6PubMed. Stingray envenomation: a retrospective review of clinical presentation and treatment in 119 cases Stingray injuries in humans usually happen when someone steps on a buried ray in shallow water, and the ray reflexively lashes its tail upward. Most stings occur on the feet or ankles for this reason.
Laboratory studies of stingray venoms have shown that the compounds involved are more biologically complex than simple pain-inducers. Venoms from whiptail stingrays demonstrated concentration-dependent effects on human cell lines, disrupting cell adhesion and triggering cell death, while a mouse fibrosarcoma cell line was markedly resistant, suggesting the venom’s molecular targets are not universally present across all cell types.7PubMed Central. Bioactive Properties of Venoms Isolated from Whiptail Stingrays and the Search for Molecular Mechanisms and Targets That selectivity is intriguing from a biomedical standpoint, though practical applications remain speculative.
Electric rays take a different approach entirely. They possess specialized organs derived from modified muscle tissue that can generate electrical discharges strong enough to stun prey or deter predators. Depending on the species, these discharges can range from mild tingles to jolts powerful enough to knock a diver off balance. Some ancient cultures actually used electric rays as a primitive form of pain relief, placing them on aching joints, though the therapeutic value was debatable at best.
Reproduction and Why It Matters for Survival
Rays reproduce in ways that are more varied than you might expect. All rays use internal fertilization, with males possessing paired claspers to deliver sperm. But what happens after fertilization diverges sharply between species. Skates are egg-layers, producing tough, leathery egg cases, sometimes called “mermaid’s purses,” that they deposit on the seafloor. The embryo develops inside the case for weeks or months before hatching.
Most rays, however, give birth to live young. Among live-bearing species, the range of strategies is striking. Some embryos develop entirely on stored yolk. Others receive supplemental nutrition from secretions produced by the uterine lining, sometimes called “uterine milk,” which function as a kind of placental substitute.8Integrative and Comparative Biology. Reproduction and Development in Chondrichthyan Fishes A few species develop a yolk-sac placenta, forming a direct nutritive connection between the mother and embryo. In all cases, though, ray litters are small. Most species produce only one to a handful of pups at a time, and gestation periods can stretch to a year or longer.
This slow reproductive rate is one of the most consequential facts about ray biology. Manta rays, for instance, are estimated to have very low productivity: they mature late, reproduce infrequently, and produce only a single pup per litter. Combined with small, localized populations and predictable seasonal aggregation patterns, this means that even modest fishing pressure can drive local declines that are difficult to reverse.9PeerJ. Diagnosing the dangerous demography of manta rays using life history theory Tropical ray species in warm, shallow waters appear to be especially vulnerable because their maximum population growth rates are intrinsically lower than those of temperate skates, making them less able to bounce back from overfishing or habitat loss.10Biological Conservation. Tropical rays are intrinsically more sensitive to overfishing than the temperate skates
Eyes, Electricity, and Color Vision
Rays interact with the world through a sensory toolkit that includes some abilities humans completely lack. Like sharks, they possess electroreceptors called ampullae of Lorenzini, clusters of jelly-filled pores on the underside of their snout that detect the faint bioelectric fields generated by the muscle contractions and heartbeats of buried prey. A stingray hunting in murky sand does not need to see its prey; it can sense the electrical signature of a hidden clam or shrimp from centimeters away.
Vision, however, is where rays differ from their shark relatives in an interesting way. While all sharks studied to date appear to be cone monochromats, meaning they likely have no color vision at all, most rays are cone dichromats, possessing two types of color-detecting cone cells. That gives rays at least a basic form of color vision, and it suggests that color perception has different survival value for bottom-dwelling, daytime-active animals than it does for the typically more pelagic and often nocturnal sharks.11PubMed Central. Vision in sharks and rays: Opsin diversity and colour vision
Ecosystem Engineers of the Seafloor
Rays are not just residents of their habitats; they actively reshape them. When bottom-dwelling rays dig into sediment to feed or rest, they churn up enormous quantities of sand and mud, a process ecologists call bioturbation. This might sound trivial until you consider the scale. In one Australian estuary, researchers estimated that rays conservatively displaced roughly 57.6 tonnes of sediment per day, or about 21 kilotonnes per year, just through routine foraging.12Remote Sensing in Ecology and Conservation. Ray bioturbation rates suggest they shape estuary processes That level of disturbance cycles nutrients through the sediment, increases oxygen penetration, and re-stratifies the layers of material on the seafloor.
Experimental work on tidal flats has shown just how quickly this matters. On one studied tidal flat, benthic rays bioturbated nearly four percent of the sediment surface per day, which translates to a complete turnover of the top sediment layer roughly every 27 days. When researchers excluded rays from test plots, sedimentation rates dropped by about 17 percent and erosion rates fell by about 43 percent. The community of small invertebrates living in the sediment also shifted, with certain worm and crustacean populations increasing in the absence of ray disturbance.13Ecosystems. Bioturbation by Benthic Stingrays Alters the Biogeomorphology of Tidal Flats The takeaway is that removing rays from coastal ecosystems does not just mean fewer rays; it changes the physical and biological character of the seafloor itself.
Cleaning Stations and the Wrasse Connection
One of the more charming aspects of manta ray behavior is their dependence on small reef fish for hygiene. Manta rays regularly visit specific sites on coral reefs, known as cleaning stations, where tiny cleaner wrasses pick parasites and dead tissue from their bodies. These visits are not casual. Research tracking manta ray movements has found that their use of reef habitats is significantly associated with the distribution of blue-streak cleaner wrasses and hard coral substrate. Cleaning interactions actually dominated habitat use at study sites, taking precedence over feeding and even courtship.14PubMed Central. Mutualism promotes site selection in a large marine planktivore
The relationship is not random or generalized. Remote video observations of giant manta rays at a seamount in the Philippines revealed that cleaner wrasses selectively foraged on the mantas’ gills and pelvic region, with some species also showing a preference for the pectoral fins, areas likely harboring higher concentrations of external parasites. Cleaning events occurred during specific hours and were constrained by current strength and water temperature. Individual manta rays even showed preferences for particular cleaning stations, potentially based on the quality of service they received there.15Marine Biology. Current strength, temperature, and bodyscape modulate cleaning services for giant manta rays For animals that spend most of their lives in open water, these reef visits represent a critical link to inshore ecosystems.
Freshwater Rays
Although most people think of rays as saltwater animals, several lineages have colonized freshwater environments. The most well-known are the river stingrays of South America, family Potamotrygonidae, which live permanently in the Amazon, Orinoco, and other river systems and never enter the sea. Getting from saltwater to freshwater is a major physiological challenge for any fish, but it is especially difficult for cartilaginous fishes, which normally rely on high concentrations of urea in their blood to maintain osmotic balance with seawater.
South American river stingrays represent the most extreme adaptation among freshwater elasmobranchs. They have eliminated the need for urea entirely, which reduces the energy they spend on nitrogen metabolism and has allowed them to lose the kidney structures that marine relatives use to conserve urea.16PubMed. Freshwater elasmobranchs: a review of their physiology and biochemistry This is not just a minor tweak; it represents a fundamental reorganization of body chemistry. Other rays that venture into brackish or freshwater, like bull sharks’ distant batoid equivalents in Southeast Asia and Australia, retain some urea-based osmoregulation and can move between salt and fresh water. The South American river rays have burned that bridge entirely and are locked into freshwater for good.
Freshwater stingrays are also popular in the aquarium trade, particularly the dramatically patterned species from the genus Potamotrygon. Their care requirements are demanding, including large tanks, warm water, soft substrates for burrowing, and careful attention to water chemistry, since they are sensitive to ammonia and nitrate levels. And because they are stingrays, they carry venomous tail spines, making them one of the few aquarium fish that can genuinely injure their keeper.
The Economics of Living Rays
One of the more compelling arguments for ray conservation comes from economics. Manta ray watching tourism has grown into a substantial global industry. A study covering 23 countries estimated that direct expenditures on manta dives exceeded 73 million US dollars annually, with the total direct economic impact reaching about 140 million dollars per year. Ten countries accounted for the vast majority of this spending, with Japan, Indonesia, and the Maldives among the largest contributors.17PLOS ONE. The Global Economic Impact of Manta Ray Watching Tourism
The Maldives offers a particularly striking case study. Manta ray tourism there has grown enormously over the past two decades. By 2021, the industry was generating an estimated 227 million US dollars in revenue when related tourist expenditure is included, representing roughly 2.6 percent of the country’s entire gross domestic product.18PubMed Central. Valuing conservation and natural wealth: The blue economy of manta ray watching in the Maldives That is a remarkable figure for a single group of animals in a single country, and it illustrates why a living manta ray is worth far more to local economies over its lifetime than a dead one sold for gill plates or meat. The growth trajectory is also notable: earlier estimates from 2006 to 2008 put direct revenue from manta diving in the Maldives at about 8.1 million dollars per year, meaning the industry grew by roughly an order of magnitude in just over a decade.19Tourism in Marine Environments. Extent and Economic Value of Manta Ray Watching in Maldives
Despite these numbers, manta and devil rays face ongoing pressure from targeted fisheries. In some regions, their gill plates are harvested for use in traditional medicine, and their meat is consumed locally. The combination of low reproductive rates and commercially motivated fishing creates a vulnerability that economic incentives from tourism alone have not fully offset, particularly in countries where fishing regulation and enforcement remain weak.
How Mantas Find Their Food
Manta rays are not just passively swimming through plankton clouds. Their foraging behavior appears to be closely tied to oceanographic conditions. Research in the Maldives has shown that manta ray aggregations at key feeding sites like Hanifaru Bay are driven by a specific combination of tidal and wind forces. Strong lunar tides, especially around new and full moons, can overcome prevailing monsoon currents and draw plankton-rich water from deeper areas outside the atoll into shallow channels. Back eddies in atoll passes then trap and concentrate zooplankton in reef inlets, creating dense feeding opportunities. The interaction between high tidal intensity and moderate winds appears to further concentrate zooplankton, setting up ideal foraging conditions.20PLoS ONE. Environmental drivers of reef manta ray (Mobula alfredi) visitation patterns to key aggregation habitats in the Maldives
This means manta ray aggregations are somewhat predictable, which is both good and bad. Predictability is what makes manta watching tourism viable; tour operators can plan excursions around lunar cycles and seasonal patterns. But predictability also makes mantas easy targets for fishers who know when and where they will show up. Protecting the specific oceanographic features that concentrate plankton, not just the rays themselves, may be essential for long-term conservation.