This revolving door of identities has long stumped scientists. It was once thought that more than 350 species of parrotfish formed the family Scaridae, but that number is closer to 80. Found in most tropical seas, parrotfish are named for their flashy, featherlike colors and birdlike grin. By day they are unstoppable eating machines. At night, some species secrete a clear mucus cocoon that cloaks their scent from predators. 

In some parrotfish species, one male can reside over a harem of females. When he dies or is displaced, the dominant female will become a male, even adopting his color, to guarantee the group’s survival. If another male moves in, that same fish may change back to female. Other species experience similar transformations, making identification tricky.

The parrotfish’s large, fused teeth illustrate how it feeds. Flexible, bony-plated jaws work like a bulldozer’s scoop, scraping and biting off crunchy coral skeletons. It’s not the hard substance they’re after, but the nutritious algae living inside the soft-bodied coral polyps. Additional jaws inside the parrotfish’s throat pulverize the indigestible coral, which then gets expelled as sand. That’s right: The beach you enjoy sinking into might be a pile of parrotfish poop! One large fish can produce a ton of sand a year.

Shedd Aquarium showcases several species of parrotfishes throughout the Caribbean Reef and the Waters of the World galleries. In case you’re wondering, the sand in their habitats in not homemade.