When our dive guide told us we had “a decent chance” of seeing manta rays, he immediately raised the stakes. Processed by the collective mind of 10 hyped-up divers, this translated as: “We will definitely see manta rays. Absolutely no doubt about it.”

An expectant hush settled on our group as the dhoni cleaved the waves on the way to our dive site, a flat reef, known in the Maldives as a thila. The boatman cut the engines and we hurried into our kit. The normally reticent woman beside me was murmuring something to nobody in particular: “If I see even one manta, I’d be happy to go home tomorrow.”

Anyone diving on a Maldivian atoll will swim past hundreds of fish. Most are ignored, some are briefly admired, but when a 14ft manta ray swoops onto a reef, it commands absolute attention. Among divers, the fish is a trump card, the very mention of its name sufficient to silence a bout of traditional après-dive bragging. And although mantas can be found all over the tropics, the Maldives is probably the most reliable place to find them all year round.

The largest of the ray family, this is quite simply the most graceful animal you will see underwater. Strong oceanic swimmers, they feed in the same manner as whales, passing plankton-rich water over their gills and sifting out the nutrients. They visit reefs to elicit the services of agreeable little fish called cleaner wrasse, which obligingly peck parasites from the rays’ bodies.

It is a sweet little arrangement: the wrasse set up shop on an area of reef that then becomes a kind of valeting station. When the mantas pick up one parasite too many, they visit a cleaning point and the wrasse enjoy a free meal. Everyone’s happy — unless a sinister interloper happens to gate-crash the party and use this symbiotic relationship for his own ends. More of that later.

WE DESCENDED through a hazy layer of surface water, heading for a recently discovered reef named Table Thila. Staying close to the others, I swam along a sandy gully, scanning the blue void beyond the reef for signs of the elusive rays.

I didn’t have long to wait. After a minute, a long, flat shape materialised from the gloom, flapping its wings lazily. It was a good-sized manta, at least 12ft across its broad pectoral fins. I stayed low, watching as it came to a halt and hovered effortlessly above a patch of reef. Quick as a flash, a dozen inch-long cleaner wrasse left the protection of the coral and swam to greet their client, who quivered with pleasure as they set about their business.

Manta rays were once held to be evil creatures. For centuries, fishermen and sailors referred to them as “devil fish”, because of the horn-like fins they use to channel water into their mouths. I prefer to think of them as angels: benign and clearly intelligent, they often approach divers out of simple curiosity. The trick is to choose a good position and let the ray take the initiative. Mantas are highly social and take a dim view of uncouth behaviour.

I was all too aware of this as I knelt on the seabed just a few feet away. I was sufficiently close to the cleaning station to be committing an egregious breach of manta etiquette. From the studied flickering of its onyx eyes, it was clear that the ray had registered my presence, yet it was happy to tolerate me as long as I didn’t disrupt its wash and brush-up.

After a few minutes, the ray took off like a flying saucer. As soon as its spot was vacated, another large ray appeared. It took up the same hovering stance and the cleaning ritual started anew. Looking back along the reef, I saw five more mantas waiting patiently — an orderly queue that would have been the pride of my local post office. Manta rays are polite creatures.

Such encounters are often fleeting, but when the animals are relaxed and the divers respect their space, the experience can last for as long as you can safely stay underwater. Such was their confidence this time, they began showing off, sailing above the heads of awestruck divers and basking in the streams of exhaled bubbles that broke across their undersides — a manta Jacuzzi.

BY THE afternoon, the tide had shifted and Table Thila was once again an ordinary reef with a lot of out-of-work cleaner wrasse. If we wanted to find more mantas, we’d have to find other waters.

Our live-aboard vessel, the Sea Spirit, moved down the west side of Ari Atoll towards a famous dive site — Madivaru Channel. When atoll water flows out into the open ocean here, Madivaru comes alive, and with a vibrancy few reefs can rival. The best approach is simply to jump in, keep the reef on your left and descend about 65ft to swim through a series of caverns, where soft coral grows in great pastel swathes. Then you gradually ascend, continuing along the reef until you reach its resident school of blue-lined snapper — another fish emblematic of Maldives diving.

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