Manta rays possess gills, which they use for both breathing and feeding. These animals belong to the class Chondrichthyes, the cartilaginous fishes, a group that also includes sharks and skates. Their impressive size, with some species reaching a wingspan of up to 23 feet, is supported by a skeleton made of cartilage rather than bone, a defining trait of their classification. Their existence relies on continuously processing large volumes of seawater to sustain their massive bodies.
The Anatomy of Manta Ray Gills
Manta rays, like all members of the subclass Elasmobranchii, feature a distinct gill structure that differs significantly from bony fish (Osteichthyes). Instead of having a single, hard bony cover known as an operculum, manta rays have multiple gill openings. They possess five pairs of gill slits, which lead directly from the pharynx to the outside environment.
These gill slits are located on the ventral, or underside, surface of the ray’s flattened body. This placement is characteristic of most rays and skates, unlike the lateral placement found in many sharks. Water enters the mouth and flows over the internal gill filaments, where oxygen is extracted, before exiting through these five slits.
The internal respiratory system consists of delicate, feathery gill filaments, which are the primary sites of gas exchange. These filaments are supported by gill arches, which form the skeletal framework of the breathing apparatus. This arrangement is fundamentally different from the single gill chamber and bony operculum of bony fish. The gills’ design allows for a high surface area for oxygen uptake, a necessity for a constantly moving, large animal.
The Mechanics of Manta Ray Respiration
The primary method manta rays use to move water across their gills for oxygen extraction is called ram ventilation. This technique relies on the animal’s constant forward motion through the water. As the manta ray swims, the pressure of the water forces a continuous stream into its wide mouth and over the respiratory surfaces of the gills.
Manta rays are considered obligate ram ventilators because they must swim continuously to breathe, a trait shared with certain fast-moving sharks. The forward movement replaces the need for muscular effort to pump water over the gills. Their spiracles, small openings behind the eyes used by some bottom-dwelling rays, are vestigial or greatly reduced, reflecting their reliance on swimming.
The constant flow of water is necessary because if a manta ray stops swimming, the flow over the gills ceases, and oxygen cannot be efficiently extracted. This constant activity dictates the manta ray’s lifestyle, as they must maintain a minimum swimming speed to sustain respiration. Young manta rays shift from a temporary buccal pumping method used in the womb to ram ventilation after birth.
How Gills Enable Filter Feeding
The gills of a manta ray serve a dual purpose, supporting both respiration and their specialized filter-feeding diet of zooplankton. As water enters the mouth, it is directed toward a unique filtration system before exiting through the gill slits. This system involves specialized structures known as gill plates, or filter pads, which are extensions of the gill arches.
These filter pads operate using a complex mechanism called “ricochet separation.” The comb-like plates are positioned to create specific fluid dynamics as water passes through them. Tiny plankton particles, even those smaller than the space between the plates, are caught in swirling eddies (vortices) and ricochet away from the gill filaments toward the esophagus.
This design ensures that the filtration system does not become clogged, which would compromise the animal’s ability to breathe. The water, stripped of plankton, continues its path over the respiratory filaments for oxygen exchange before being expelled through the gill slits. This simultaneous process allows the manta ray to feed and breathe efficiently while constantly swimming, consuming vast amounts of plankton.