Many years ago, long before I became acquainted with Bermuda’s glorious aquatic colours, I bought a piece of cloth to make myself a winter dress.

When I took it home, my mother and grandmother showed instant disapproval. The material was a close weave of blue and green, giving an overall effect of turquoise. “Ah,” they said sadly, “blue and green should never be seen.” They were not alone in their opinion—it seemed to be a fashion truism. But I was never able to understand why. Aren’t blue and green nature’s favourite colours?

I gave their pronouncement no more thought until 1970 when I got to meet Bermuda and my very first parrotfish. We were walking on the edge of Horseshoe Bay at the time when Mike pointed to a wave. It was rising to a curl and below its crest a fish was riding through it. Blue and green should never be seen? It was beautifully, iridescently blue, shining through the green of the water.

Later I came to learn more about their colour schemes. There are apparently at least 13 different kinds of parrotfish in Bermuda, but sometimes it’s difficult to distinguish which is which, particularly as some change colour throughout their lives. Stoplight parrotfish, for example, both male and female, start off reddish brown with bright red bellies, brownish dorsal fins and bright red pectoral fins. As the creatures grow older, their bellies fade and a white bar appears on the tail fin. But there’s an added complication. Some females change gender, becoming “secondary” or “terminal” males, and when they do, they become red, yellow and, yes, bright green and blue. This sex change seems to happen when the dominant male disappears or when there’s a lack of breeding males or females. Primary males mate in small groups containing one male and several females, but the secondary male pairs with just one female.

Beautiful though parrotfish colours are, I have to say their teeth are downright scary. That’s because they’re fused and look more like the beaks of parrots rather than teeth—thus the name parrotfish. Gliding in and out of the reef, they use their “beaks” to scrape off algae and bits of coral and let a second set of teeth in the back of their throats grind any coral skeletal material they might ingest.

William Beebe describes seeing them from his bathysphere a mile off Bermuda in 1931 in his book Half a Mile Down. “The giant caerulean [blue] browse on hard coral as a horse tears off mouthfuls of grass.”

Snorkelers all agree they can hear them feeding—a crepitation, a cross between a crackling and the grating sound of broken bone. They can also often see the fish expel a cloud of dust through their digestive systems, creating mounds of white sand. So these fish are not just decorative; they can produce a ton of coral sand per acre of reef each year, and they help clean surfaces on the reef on which new organisms can grow.

As Beebe explains, other fish return the favour: “Once I saw an interesting exchange of courtesy, one which I observed many times when diving near shore. After an interval of feeding, when the teeth and jaws and scales of the head are covered with debris, the [parrot] fish upends in mid-water and holds itself motionless while a school of passing wrasse, all tiny in comparison with the big fish, rush from all sides and begin a systematic cleaning of the large fish’s head.”

I envy Beebe and snorkelers, too. Being definitely far more mountain goat than fish, a Capricorn, not a Pisces, I am never at home swimming in the water. So I am grateful to parrotfish for sometimes making themselves visible to me when I’m standing by rocks in the water near the shoreline. But I can’t help wondering, as I watch them use their pectoral fins to glide in and out of rocky crevices, whether maybe looking at me, they share Leigh Hunt’s fish’s view of a human:

O flat and shocking face,
Grimly divided from the breast below!
Thou that on dry land horribly dost go
With a split body and most ridiculous pace,
Prong after prong, disgracer of all grace,
Long-useless-finned, haired, upright, unwet, slow!