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Unbelievable Parrotfishes Live Here

If you’ve ever enjoyed digging your toes into the fine white sand of a tropical beach, you have parrotfishes to thank.

These relatives of wrasses use their unique beaklike fused teeth—from which they get their common name—to scrape algae from corals. At the same time, parrotfishes also munch and crunch bits of stony coral skeleton. An additional set of molarlike teeth in their throats pulverizes the coral and the nutrients are digested.

The rest is expelled in a cloud of waste that includes the most beautiful sand in the world.

The stoplight parrotfish, a long, rotund fish about the length of a forearm, can change its coloring.

And it piles up quickly. Parrotfishes move in large schools and spend up to 90 percent of the day grazing—and processing. Estimates vary (as do the sizes of parrotfish species, from 1 to 4 feet) on how much sand one fish generates in a year, from around 200 to 700 pounds.

Parrotfishes’ diet and digestion make them critical to the health of two essential coastal habitats. They protect coral reefs, from the Caribbean to the Indo-Pacific, by controlling algae, which otherwise would overgrow and kill corals. And they are beach builders, countering erosive wave action on shorelines with their prodigious powdery outputs.

According to a Scientific American article, researchers have identified parrotfishes as major producers of island-building sediment in the Maldives. This nation of nearly 1,200 coral atolls in the Indian Ocean is at risk of being inundated by rising sea levels. So these bucktoothed browsers are combatting the effects of global climate change too.

But that’s just the start of parrotfishes’ unbelievableness.

Poop is good, poison not so much

Some of the things parrotfishes eat can make eating them hazardous to your health. They are among the many reef species that might ingest a tiny toxic organism as they graze. It doesn’t affect the fishes, but the potent toxin accumulates in their tissues, is undetectable and survives cooking, leading to the gastrointestinal and neurological horrors of ciguatera poisoning for unsuspecting diners. Pass on the parrotfish—we need them too much on coral reefs anyway.

A stoplight parrotfish in Caribbean Reef opens its mouth to display its iconic large front tooth for crunching down on corals.

Parrotfish jammies

Several species, including the princess parrot, which you can see in the Caribbean Reef, tuck themselves in each night by blowing a clear mucous bubble that envelopes the whole body. Like an invisible shield, it protects the fishes from blood-sucking parasites and nocturnal predators like moray eels and sharks

A stoplight parrotfish, its conical head tilted towards the viewer, in Caribbean Reef.

A stoplight parrotfish in the typical red to brown coloration of a female.

A male stoplight parrotfish swims by in Caribbean Reef.

A stoplight parrotfish in the blue and green coloration of a male.

Shifting sexes

Most parrotfishes are protogynous sequential hermaphrodites. If that sounds complicated, it is.

In almost all parrot species, the young start out as females that have the ability to change into males as they age. The female stage of life is called the initial phase and the male the terminal phase. Sex shifts occur as the need or opportunity arises within parrotfishes’ harem social structure.

The large schools, which can number as many as 40 individuals, are led by one (formerly female) dominant male that has exclusive breeding privileges with the females. When that male dies, the largest female in the school begins the several-weeks-long transition into the new dominant male and new role.

The sex shifts are accompanied by such dramatic changes in color and pattern that early naturalists unwittingly assigned the males and females of the same species to separate taxonomic groups. The stoplight parrotfishes above are shown in both the typical red to brown coloration of a female and the eye-popping aqua coloration of a male. Depending on the species, the terminal-phase fish can also be vivid green or electric blue, with hot pink or chrome yellow markings. Juveniles have their own color patterns, and some species have the chameleonlike ability to change hue to mimic other fishes.

The stoplight parrot is one of a number of parrotfish species in which the young can also develop directly into males, although they can still look like initial-phase females. And in one parrotfish species, the fish stick to their birth sex.

An animal care staff member holds out a stack of four cylindrical, chunky plaster cakes, made up of chalky white plaster embedded with various vegetables, with a dark coating of nori on top.

Plaster cakes resemble coral formations, allowing the fishes to feed naturally, which includes beneficial tooth grinding.

A pufferfish is held gently in a white-gloved hand with its head lifted from the water in Shedd's Animal Hospital, as another Animal Care staff member gently shaves down its large teeth with a dremel tool.

A pufferfish has its teeth cleaned and trimmed in Shedd's Animal Hospital.

Totally gnawsome

Parrotfishes’ coral-chomping choppers grow continuously, a necessary adaptation to offset the extreme wear and tear of the fishes’ eating habits. In aquariums, where the corals in habitats are typically on exhibit rather than on the menu, animal care staffers must maintain the fishes’ teeth. That could include a veterinarian occasionally using a Dremel tool to trim the teeth. But Shedd’s aquarists concocted a more natural solution: plaster cakes.

Culinary creativity for the animals is widespread through the aquarium: ice cakes for the sea otters, nori rolls for the sea turtle. The parrots’ plaster cakes start, appropriately enough, with a batter of dental plaster. Shredded carrots, sweet potatoes and dried seaweed are stirred in, and it’s all topped with a bit of nori. After the mixture dries overnight, the cakes are dropped into the parrots’ habitats. The treats now resemble coral formations, allowing the fishes to feed naturally, which includes beneficial tooth grinding. (The harmless, calcium-compound dental plaster gets ground up in the digestive process and passes through the fish the same way calcium-carbonate coral does.)

Look for several species of parrotfishes in the Caribbean Reef and the iguana habitat in the Islands and Lakes gallery. They’re among many animals with unbelievable characteristics and adaptations that you’ll encounter at Shedd Aquarium.