with rolled up cephalic fins and characteristic dorsal coloration (
Ko Hin Daeng, Thailand
Side view of M. birostris
with unfolded cephalic fins (
Ko Hin Daeng, Thailand
The giant oceanic manta ray can grow to a disc size of up to 7 m (23 ft) across with a weight of about 3,000 kg (6,600 lb) but average size commonly observed is 4.5 m (15 ft). It is dorsoventrally flattened and has large, triangular pectoral fins on either side of the disc.
At the front, it has a pair of cephalic fins which are forward extensions of the pectoral fins. These can be rolled up in a spiral for swimming or can be flared out to channel water into the large, forward-pointing, rectangular mouth when the animal is feeding.
The teeth are in a band of 18 rows and are restricted to the central part of the lower jaw.
The eyes and the spiracles are on the side of the head behind the cephalic fins, and the gill slits are on the ventral (under) surface.
It has a small dorsal fin and the tail is long and whip-like. The manta ray does not have a spiny tail as do the closely related devil rays (Mobula spp.) but has a knob-like bulge at base of its tail.
The skin is smooth with a scattering of conical and ridge-shaped tubercles. The colouring of the dorsal (upper) surface is black, dark brown, or steely blue, sometimes with a few pale spots and usually with a pale edge. The ventral surface is white, sometimes with dark spots and blotches. The markings can often be used to recognise individual fish.
Manta birostris is similar in appearance to Manta alfredi and the two species may be confused as their distribution overlaps. However, there are distinguishing features.
Physical distinctions between oceanic manta ray and reef manta ray
The oceanic manta ray is larger than the reef manta ray, 4 to 5 meters in average against 3 to 3.5 meters. However, if the observed rays are young, their size can easily bring confusion. Only the color pattern remains an effective way to distinguish them. The reef manta ray has a dark dorsal side with usually two lighter areas on top of the head, looking like a nuanced gradient of its dark dominating back coloration and whitish to greyish, the longitudinal separation between these two lighter areas forms a kind of "Y". While for the oceanic manta ray, the dorsal surface is deep dark and the two white areas are well marked without gradient effect. The line of separation between these two white areas form meanwhile a "T".
Difference can also be made by their ventral coloration, the reef manta ray has a white belly with often spots between the branchial gill slits and other spots spread across trailing edge of pectoral fins and abdominal region. The oceanic manta ray has also a white ventral coloration with spots clustered around lower region of its abdomen. Its cephalic fins, inside of its mouth and its gill slits are often black.