Parrotfish are reef engineers. By scraping algae off the coral, they keep the reef healthy and clear. A single parrotfish can produce hundreds of kilograms of sand per year. Scientists estimate that much of the white sand on tropical beaches was created by parrotfish over thousands of years.
At night, some parrotfish wrap themselves in a bubble of mucus - like a sleeping bag made of slime - which helps disguise their scent from predators while they sleep. In the morning, they break out of the bubble and start nibbling the reef again.
Parrotfish can change colour as they grow, and some species can even change sex during their lifetime. The males are often the most brilliantly coloured, flashing electric blue and turquoise as they dart over the reef. Around Nauru's coast, snorkellers sometimes get to swim right alongside them.