Stingrays, like sharks and skates, are cartilaginous fish known as elasmobranchs. While they appear to glide silently along the ocean floor, they possess a sophisticated suite of sensory organs. They lack visible external ears, but stingrays possess complex internal structures for hearing and balance. Their unique sensory world combines sound detection, mechanical sensing, and the ability to perceive electrical fields.
How Stingrays Hear Without External Ears
Sound travels effectively through water, and the stingray’s entire body acts as a receiver for vibrations. Since the body is composed of cartilage, sound waves pass directly through the tissues and skull to the inner ear. This direct vibration transfer allows the stingray to detect the particle motion component of sound, as they lack the air-filled swim bladder used by many bony fish.
The inner ear is a fluid-filled labyrinth located within the skull, responsible for both hearing and maintaining equilibrium. It contains three orthogonally arranged semicircular canals, which primarily detect rotational movements and angular acceleration, providing the ray’s sense of balance. Specialized structures within the inner ear, such as the sacculus and the macula neglecta, are the primary detectors of sound.
These auditory structures contain sensory hair cells stimulated by the movement of dense particles, called otoliths, within the fluid. When sound waves cause the stingray’s body to vibrate, these hair cells are deflected, translating physical motion into nerve signals. The macula neglecta is highly sensitive to vertical movements and vibrations transmitted through the substrate, which is crucial for a bottom-dwelling animal. Stingrays are most sensitive to low-frequency sounds, generally between 50 and 1000 Hertz, a bandwidth that includes sounds made by struggling prey or distant predators.
Sensing Pressure and Movement with the Lateral Line
Hearing is only one part of the stingray’s mechanosensory system; they also rely heavily on the lateral line system to “feel” their immediate environment. This system is a network of tiny fluid-filled canals and pores running across the body, concentrated on both the dorsal and ventral surfaces. These canals contain sensory cells called neuromasts, which are composed of hair cells embedded in a gelatinous structure known as a cupula. The lateral line detects minute changes in water pressure, currents, and nearby movement, allowing the ray to perceive the hydrodynamic wake of other organisms.
When water movement displaces the fluid in the canals, it deflects the cupula and stimulates the hair cells, sending a signal to the brain. This system is especially important for stingrays that spend time in murky water or hunt prey buried in the sand.
The distribution of the lateral line system is adapted to the stingray’s flattened body and benthic lifestyle. The ventral (bottom) canals are particularly important; some non-pored sections function as specialized tactile mechanoreceptors to detect prey movements directly against the skin. This allows the ray to detect the weak water jets produced by buried bivalves or the slight movements of other invertebrates. In some species, the tail also functions as a hydrodynamic sensory antenna, extending the ray’s ability to sense its surroundings.
The Electric Sense of Elasmobranchs
A specialized sense is electroreception, mediated by the Ampullae of Lorenzini, a defining feature of all elasmobranchs. These organs are a network of jelly-filled canals that originate from pores scattered across the skin, particularly on the head and around the mouth. Each canal terminates in a small bulb containing sensory cells.
The Ampullae of Lorenzini detect extremely weak electrical fields in the surrounding seawater. Living organisms, including buried prey, generate minute bioelectric fields from muscle contractions, nerve impulses, and ion exchange across the gills. This sense is incredibly acute, allowing stingrays to detect electrical gradients as low as 1 to 5 nanovolts per centimeter.
This electrosense functions as a highly precise targeting mechanism during hunting. A stingray uses its lateral line to locate the general area of a buried creature, then uses the Ampullae of Lorenzini to pinpoint the exact location of the prey’s electrical signature for the final strike.