Roughly 80 species of parrotfish exist, all of them belonging to the taxonomic family Scaridae. They're mostly found in tropical waters across the Atlantic, Indian and Pacific oceans, but some types also live in subtropical waters. Although distinct species, they all have some common adaptations and similar social and reproductive relationships.
Talking About Teeth
The name "parrotfish" comes from their fused, beak-like front teeth. These teeth aren't just for show, they're a useful adaptation that allow these fish to eat algae that lives on coral, and even the coral itself. While they can use the teeth to carefully scrape off and consume algae, they're also strong enough to bite off large chunks of coral. They can then use a second set of teeth in their throats to grind down the coral into chunks small enough to be swallowed. It's unclear whether they extract algae or coral polyps from the coral they digest.
An unusual adaptation that most parrotfish share is the ability to change gender from female to male. In some species, all parrotfish hatch out as females and some later turn into males. However, in the majority of cases, a mixture of females and males are hatched and females will only change gender if the need for more males in an area arises. If too few males exist, females' eggs could go unfertilized and the population could decline.
Parrotfish generally have a complex social structure. Although a few exceptions exist, most species live in large groups of roughly 40 members. These groups usually consist of a harem of females, led by just one male. The sexually mature male leading the group is sometimes referred to as a terminal male or supermale. When the male dies, one of the females in his harem will usually change gender to replace him.
Mating and Reproductive Relationships
Parrotfish reproduce through external fertilization. Females lay their eggs into the open water, and males must fertilize them by releasing sperm in their vicinity. Those species that live in a harem will usually reproduce within the group, the supermale fertilizing the eggs of all his females. However, males who don't have their own harems will sometimes sneak into the group and attempt to pair up and mate with one of the females or just release his sperm around a spawning pair, with hope that his gametes will fertilize some of the eggs.