Stingrays belong to the Myliobatiformes order, a group of cartilaginous fish (elasmobranchs) closely related to sharks. These marine animals possess a dramatically flattened body plan, forming a disc shape highly specialized for life on the ocean floor. This benthic (bottom-dwelling) existence has shaped their physical structure, including a sensory system adapted for camouflage and finding prey in low-visibility environments. Their entire physiology, from respiration to vision, reflects this singular adaptation to the seabed.
Dorsal Eye Placement and Related Anatomy
The eyes of the stingray are located on the dorsal, or top, surface of their flattened body disc, an unusual placement for a fish. This position allows the ray to monitor its surroundings for potential threats even when concealed under sand or sediment. The ventral, or underside, of the ray’s body is dedicated to feeding and respiration, making dorsal eye placement necessary for surveillance.
Directly behind each eye is a specialized opening called a spiracle, often mistaken for a second pair of eyes. Spiracles enable the stingray to breathe while resting or buried on the seabed. Since the ray’s five pairs of gill slits are located on the underside and would be blocked by the substrate, the spiracles draw clean water directly from above.
Water pulled through the spiracles is passed over the gills for gas exchange, allowing the ray to remain hidden for extended periods. This respiratory system supports the ray’s reliance on camouflage to avoid predators and ambush prey.
Visual Acuity and Field of View
Stingrays possess eyes highly adapted for the low-light conditions characteristic of their murky, benthic environment. Their retinas contain a high proportion of rod photoreceptors compared to cone photoreceptors. This rod dominance enhances their scotopic, or night vision, making them effective at detecting movement in dim light.
This specialization for low light comes at the cost of visual sharpness, or acuity. Studies on freshwater stingrays indicate a relatively low visual resolution, with acuity measurements ranging from less than 0.13 to 0.23 cycles per degree. Compared to many other fish, their ability to discern fine detail is limited.
The placement of the eyes on the top and sides of the head grants the stingray an expansive, nearly 360-degree field of view. This wide field is primarily used for surveillance, allowing the animal to detect large shadows or movements from predators swimming above them. While some species can discriminate colors and shapes, vision is not the primary tool for detailed hunting.
The eyes are better suited for general environmental monitoring due to the limited utility of detailed vision in their dim, sediment-filled habitat. The retina often features a dorsal retinal streak, an area of higher cell density that enhances acuity in the ventral visual field. This specialization enables the ray to scan the substrate below for prey as it moves, despite its generally low overall visual acuity.
Non-Visual Senses Used for Navigation and Hunting
Because their vision is primarily suited for detecting predators, stingrays rely on highly developed non-visual senses to navigate and locate prey buried in the sand. The most remarkable is electroreception, facilitated by specialized sensory organs called the Ampullae of Lorenzini. These organs are a network of jelly-filled pores concentrated around the ray’s snout and mouth area.
The Ampullae of Lorenzini detect minute electrical fields generated by the muscle contractions and biological processes of other organisms. This allows the stingray to sense prey, such as small fish, crabs, and mollusks, even when hidden beneath the substrate. The sensitivity of these electroreceptors is high, capable of detecting charges as low as 0.01 microvolts per centimeter.
Stingrays also use chemoreception (smell and taste) to track down food. Their nostrils, or nares, are located on the underside of their head and detect chemical cues in the water. They also possess a lateral line system, a series of fluid-filled canals along their body that detect changes in water pressure and vibrations.
The lateral line system provides information about water movement, essential for close-range navigation and detecting disturbances caused by nearby prey. These three non-visual senses—electroreception, chemoreception, and mechanoreception—collectively compensate for the limitations of their vision, creating a multi-modal sensory profile tailored for life on the ocean floor.