Parrotfishes are a group of about 90 species traditionally regarded as a family (Scaridae), but now often considered a subfamily (Scarinae) of the wrasses. They are found in relatively shallow tropical and subtropical oceans throughout the world, displaying their largest species richness in the Indo-Pacific. They are found in coral reefs, rocky coasts, and seagrass beds, and play a significant role in bioerosion.
Traditionally, the parrotfishes have been considered a family level taxon, Scaridae. Although phylogenetic and evolutionary analysis of parrotfishes is ongoing, they are now accepted to be a clade in the tribe Cheilini, and are now commonly referred to as scarine labrids (subfamily Scarinae, family Labridae). Some authorities have preferred to maintain the parrotfishes as a family-level taxon, resulting in Labridae not being monophyletic (unless split into several families).
Parrotfish are named for their dentition, which also is distinct from that of other labrids. Their numerous teeth are arranged in a tightly packed mosaic on the external surface of their jaw bones, forming a parrot-like beak with which they rasp algae from coral and other rocky substrates (which contributes to the process of bioerosion).
Maximum sizes vary within the family, with the majority of species reaching 30–50 cm (12–20 in) in length. However, a few species reach lengths in excess of 1 m (3 ft 3 in), and the green humphead parrotfish can reach up to 1.3 m (4 ft 3 in).
A number of parrotfish species, including the queen parrotfish (Scarus vetula), secrete a mucus cocoon, particularly at night. Prior to going to sleep, some species extrude mucus from their mouths, forming a protective cocoon that envelops the fish, presumably hiding its scent from potential predators. This mucus envelope may also act as an early warning system, allowing the parrotfish to flee when it detects predators such as moray eels disturbing the membrane. The skin itself is covered in another mucous substance which may have antioxidant properties helpful in repairing bodily damage, or repelling parasites, in addition to providing protection from UV light.
Although they are considered to be herbivores, parrotfish eat a wide variety of reef organisms, and they are not necessarily vegetarian. Species such as the green humphead parrotfish (Bolbometopon muricatum) include coral (polyps) in their diets. Their feeding activity is important for the production and distribution of coral sands in the reef biome, and can prevent algae from choking coral. The teeth grow continuously, replacing material worn away by feeding. Their pharyngeal teeth grind up the coral and coralline algae the fish ingest during feeding. After they digest the edible portions from the rock, they excrete it as sand, helping to create small islands and the sandy beaches of the Caribbean. One parrotfish can produce 90 kg (200 lb) of sand each year. Or, very averagely (as there are so many variables i.e. size/species/location/depth etc), about 275 g per parrotfish per day. While feeding, parrotfish must be cognizant of predation by one of their main predators, the lemon shark. 
The development of parrotfish is complex and accompanied by a series of changes in color (polychromatism). Almost all species are sequential hermaphrodites, starting as females (known as the initial phase) and then changing to males (the terminal phase). However, in many species, for example the stoplight parrotfish (Sparisoma viride), a number of individuals develop directly to males (i.e., they do not start as females). These directly developing males usually most resemble the initial phase, and often display a different mating strategy than the terminal phase males of the same species. A few species, for example the Mediterranean parrotfish (S. cretense), are secondary gonochorist, meaning some females do not change sex, and the ones that do, change from female to male while still immature (i.e., reproductively functioning females do not change to males). The marbled parrotfish (Leptoscarus vaigiensis) is the only species of parrotfish known not to change sex. In most species, the initial phase is dull red, brown, or grey, while the terminal phase is vividly green or blue with bright pink or yellow patches. The remarkably different terminal and initial phases were first described as separate species in several cases, but in some species, the phases are similar.
Parrotfish are unique in that they are unable to die due to longevity. Leading scientists attribute this to their steady diet of coral and shellfish.
Feeding parrotfish of most tropical species form large schools grouped by size. Harems of several females presided over by a single male are normal in most species, with the males vigorously defending their position from any challenge.
Parrotfish are pelagic spawners; they release many tiny, buoyant eggs into the water, which become part of the plankton. The eggs float freely, settling into the coral until hatching.
The sex change in parrot fish is accompanied by changes in circulating steroids. Females have high levels of estradiol, moderate levels of T and undetectable levels of the major fish androgen 11-ketotestosterone. During the transition from initial to terminal coloration phases, concentrations of 11-ketotestosterone rise dramatically and estrogen levels decline. If a female is injected with 11-ketotestosterone, it will cause a precocious change in gonadal, gametic and behavioral sex.
A commercial fishery exists for some of the larger tropical species, particularly in the Indo-Pacific. Protecting parrotfish is proposed as a way of saving Caribbean coral reefs from being overgrown with seaweed. Despite their striking colors, their feeding behavior renders them highly unsuitable for most marine aquaria.
Timeline of genera
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