In this Minute of tranquillity, we’d like to introduce you to one of the ocean’s most recognisable icons, the reef manta ray. The species was described in 1868 by Gerard Krefft, the director of the Australian Museum. He named it M. alfredi in honour of Alfred, Duke of Edinburgh, the first member of the British royal family to visit Australia. It was originally described as part of the genus Manta but in 2017 was changed, along with the other manta species, to be included as part of the genus Mobula. The artist formerly known as Manta alfredi, is as famous, as it is graceful. This gentle giant is the smaller of the two manta species currently known to science.
Despite their distinctive flattened body, this fish is closely related to sharks. 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 eyes and the spiracles are on the side of the head behind the cephalic fins, and the five-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 their close relatives, the devil rays (Mobula spp.). The colour of the dorsal side is dark black to midnight blue with scattered whitish and greyish areas on the top head. The ventral surface is white, sometimes with dark spots and blotches. The markings can often be used to recognise individual fish. Mobula alfredi is similar in appearance to Mobula birostris and the two species may be confused as their distribution overlaps. However, there are distinguishing features.
The first difference is the size. M. birostris is bigger than the reef M. alfredi, 4 to 6 m on average vs. 3 to 4 m. However, when they’re young specimens telling them apart becomes somewhat difficult, in which case only the colour pattern remains an effective way to distinguish them. The reef manta 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 colouration and whitish to greyish, the longitudinal separation between these two lighter areas forms a kind of “Y”. While for the oceanic manta, the dorsal surface is deep dark and the two white areas are well marked without gradient effect. Meanwhile, the line of separation between these two white areas forms a "T". Also, the reef manta ray has a white belly with often spots between the branchial gill slits and other spots spread across the trailing edge of the pectoral fins and abdominal region. The oceanic manta has also a white ventral colouration with spots clustered around the lower region of its abdomen. Its cephalic fins, the inside of its mouth and its gill slits are often black.
Both species have the largest brain of all known fish species and are very curious and intelligent. Because of its large size and velocity in case of danger (24 km/h escape speed), the reef manta has very few natural predators which can be fatal to it, apart from some large shark species and orcas. Since there’s so much to tell about this beautiful creature, more info will follow in future Manta Minutes …
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