Stingrays, flattened relatives of sharks and skates, possess a pair of functional eyes despite their bottom-dwelling lifestyle. These unique cartilaginous fish often rest camouflaged on the ocean floor, where their visual organs play a specific role in their survival. The question of whether they have eyes is often tied to confusion about other prominent features on their bodies. They are found across tropical and temperate marine waters worldwide.
The Location and Function of Stingray Eyes
Stingray eyes are positioned on the dorsal surface of their wide, disc-shaped bodies. This placement is strategic, given their habit of settling directly on the seafloor, sometimes partially buried in the sediment. The positioning means their eyes primarily scan the water column above them rather than the sand directly below. Their vision is not considered sharp. The eyes function mainly to spot potential threats, such as large sharks or other predators, swimming overhead. Some species have adaptations like a reflective layer in the retina, known as the tapetum lucidum, which helps increase light sensitivity in dim underwater conditions.
Distinguishing Eyes from Spiracles
A common source of confusion is the pair of large openings situated very close to and slightly behind the eyes. These prominent features are not a second set of eyes but are called spiracles. Many observers mistake the spiracles for the ray’s visual organs because of their size and proximity to the actual eyes on the dorsal side.
The spiracles serve a crucial respiratory function, acting as an intake valve for water. When a stingray is resting or buried in the sand, its mouth and gill slits, located on the ventral (underside) surface, are pressed against the substrate. The spiracles allow the ray to draw in clean, sediment-free water from above, which is then passed over the gills for gas exchange. This adaptation is particularly important for sand-dwelling species, as it prevents the gills from becoming clogged with debris.
Advanced Sensory Systems
Because a stingray’s eyes offer limited utility for locating food buried in the sand, the animal depends on specialized non-visual senses for hunting. This reliance on other senses explains how they can successfully find prey even when completely concealed beneath the sediment. They are equipped with a highly sensitive electrosensory system, shared with their relatives, the sharks.
This system uses a network of minute, jelly-filled pores, mostly concentrated on the underside of their disc near the mouth, which are capable of detecting weak electrical fields. Every living organism generates a faint electrical signature from muscle contractions and nerve activity. The stingray can use these sensors to pinpoint the exact location of a crab, clam, or small fish hidden beneath the sand.
In addition to electroreception, stingrays possess a mechanosensory lateral line system that detects minute vibrations and changes in water pressure. This system consists of canals and pores running across the body. It can sense the small jets of water expelled by buried prey as they breathe or move. These two advanced sensory tools allow the stingray to effectively navigate and hunt in dark, murky, or sandy environments.