Mantas can be found in temperate, subtropical and tropical waters. Both species are pelagic; M. birostris migrates across open oceans, singly or in groups, while M. alfredi tends to be resident and coastal. They are filter feeders and eat large quantities of zooplankton, which they swallow with their open mouths as they swim. Gestation lasts over a year, producing live pups. Mantas may visit cleaning stations for the removal of parasites. Like whales, they breach, for unknown reasons.
Both species are listed as Vulnerable by the International Union for Conservation of Nature. Anthropogenic threats include pollution, entanglement in fishing nets, and direct harvesting for their gill rakers for use in Chinese medicine. Their slow reproductive rate exacerbates these threats. They are protected in international waters by the Convention on Migratory Species of Wild Animals, but are more vulnerable closer to shore. Areas where mantas congregate are popular with tourists. Only a few aquariums are large enough to house them. In general, these large fish are seldom seen and difficult to study.
Appearance and Anatomy
Manta rays are known for their large size, broad heads, triangular pectoral fins, and the horn-shaped cephalic fins located on either side of their mouths. They have horizontally flattened bodies with eyes on the sides of their heads (behind the cephalic fins) and gill slits on their ventral surfaces. Their tails lack skeletal support and are shorter than their disc-like bodies. The dorsal fins are small and at the base of the tail. The largest mantas can reach 1,350 kg (3,000 lb). In both species the width is approximately 2.2 times the length of the body; M. birostris reaches at least 7 m (23 ft) in width while M. alfredi reaches about 5.5 m (18 ft). Dorsally, mantas are typically black or dark in color with pale markings on their "shoulders". Ventrally, they are usually white or pale with distinctive dark markings by which individual mantas can be recognized. All black color morphs are known to exist. The skin is covered in mucus which protects it from infection.
Mantas move through the water by the wing-like movements of their pectoral fins, which drive water backwards. Their large mouths are rectangular, and face forward as opposed to other ray and skate species with downward-facing mouths. The spiracles typical of Chondrichthyes are vestigial, and mantas must swim continuously to keep oxygenated water passing over their gills. The cephalic fins are usually spiralled, but flatten during foraging. The fish's gill arches have pallets of pinkish-brown spongy tissue that collect food particles. Mantas track down prey with visual and olfactory senses. They have one of the highest brain-to-body mass ratios of all fish, and their rete mirabiles may serve to keep the brain warm.
