The term “devil fish” evokes a dramatic image of a monstrous creature lurking in the deep, a sensational name given to large marine life with a striking appearance. However, the animal most closely associated with this moniker is not a sea monster but a gentle giant: the Mobulid ray. This common name is primarily used for rays whose unusual physical features led to a history of fear and misunderstanding.
Identifying the Devil Fish
The modern scientific focus for the “devil fish” is the family Mobulidae, which encompasses the well-known manta rays and the smaller devil rays. Until recently, manta rays belonged to the genus Manta, while their relatives were grouped in Mobula, leading to confusion in nomenclature. A comprehensive 2017 genetic study revealed the two groups are far more closely related than previously thought, resulting in the reclassification of all manta rays into the genus Mobula.
This means the Giant Oceanic Manta (Mobula birostris), the Reef Manta (Mobula alfredi), and the Atlantic Manta (Mobula yarae) are all now classified under Mobula. The former manta species are significantly larger, reaching wingspans of up to 20 to 30 feet, and have a terminal mouth positioned at the front of the body. The smaller, traditional devil rays feature a subterminal mouth located slightly behind the front of the head, but all species share the distinctive “horns” that earned them the common name.
The Distinctive Anatomy
The physical feature responsible for the dramatic common name is a pair of paddle-like appendages known as cephalic fins, which extend forward from the ray’s head on either side of the mouth. When curled inward, these fins can resemble the horns of a devil, especially when viewed from below by ancient mariners.
The primary purpose of these cephalic fins is to funnel plankton-rich water directly into the ray’s wide opening. The rays maneuver these fins with precision, unfurling them to create a scoop when feeding on tiny organisms like zooplankton. The fins are also used for communication, with rays subtly curling and uncurling them to signal to other individuals, particularly at communal cleaning stations. The main body, or disc, is characterized by a flattened, rhomboid shape, propelled through the water by large, wing-like pectoral fins.
Behavior and Dispelling the Danger Myths
Despite the terrifying moniker and immense size, these rays are gentle, docile planktivores that pose no threat to humans. Their diet consists exclusively of plankton, which they filter from the water as they swim. Historical myths of “devil fish” attacking boats or wrapping divers in their wings are unfounded stories fueled by fear of the unknown.
Their interactions with humans are often characterized by curiosity, with individuals sometimes approaching divers or snorkelers for inspection. One of the most spectacular Mobulid behaviors is breaching, where the rays propel themselves entirely out of the water, sometimes flipping and landing with a loud clap. While the exact reasons for this behavior are not fully understood, theories suggest it may be a form of long-distance communication, part of a courtship ritual, or a method for dislodging irritating parasites.
Global Range and Conservation Status
Mobulid rays inhabit tropical and temperate waters worldwide, with different species occupying distinct ecological niches, from coastal reefs to the open ocean. The giant oceanic manta, Mobula birostris, is a highly migratory species that travels vast distances. Other species, like the Reef Manta, Mobula alfredi, tend to remain in more localized coastal areas.
Despite their global distribution, many Mobulid species face significant population declines and are listed as Vulnerable or Endangered on the IUCN Red List. The single greatest threat is overfishing, driven by the international trade in their gill rakers. These delicate filtering structures are dried and sold primarily in Asian markets for use in a purported health tonic, despite having no proven medicinal value. Because females typically produce only one pup every few years, these populations are extremely susceptible to fishing pressures, leading to rapid declines.