Parrotfish

Parrotfish
Scarus frenatus
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Superclass:	Osteichthyes
Class:	Actinopterygii
Order:	Perciformes
Suborder:	Labroidei
Family:	Scaridae Rafinesque, 1810
Genera
Bolbometopon Calotomus Cetoscarus Chlorurus Cryptotomus Hipposcarus Leptoscarus Nicholsina Scarus Sparisoma

Parrotfish are a large group of marine species inhabiting shallow coastal waters in tropical and subtropical oceans throughout the world. 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.

Taxonomy

Chlorurus microrhinos from the north coast of East Timor

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).

Description

Parrotfish are named for their dentition, which is distinct from other fishes, including 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). One of the smallest species bluelip parrotfish (Cryptotomus roseus), only reaches 13 cm (5.1 in).

Mucus

Some 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.

Feeding

The strong beak of Bolbometopon muricatum is able to grind the sturdiest corals.

Parrotfish are detritivores and eat a wide variety of microscopic organisms living on and within the substrate. 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 algal overgrowth of the reef structure. 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. The green humphead 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. On Caribbean coral reefs, parrotfish are important consumers of sponges. An indirect effect of parrotfish grazing on sponges is the protection of reef-building corals that would otherwise be overgrown by fast-growing sponge species.

Life cycle

The bicolor parrotfish (Cetoscarus bicolor) was described by Rüppell in 1829. In 1835, he mistakenly described the terminal phase, featured on this photo, as a separate species, C. pulchellus

The development of parrotfishes is complex and accompanied by a series of changes in color (polychromatism). Most species are sequential hermaphrodites, with the majority of species beginning life as females and then changing to males. Some species are gonochoristic developing from male juveniles to female adults. The best example is the mediterranean parrotfish, Sparisoma cretense, where the colourful adults are female and the drab grey colored intermediate phase fishes are male. However, in other 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. The marbled parrotfish (Leptoscarus vaigiensis) is the only species of parrotfishes 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.

In most parrotfish species, juveniles have a different color pattern from adults. Juveniles of some tropical species can alter their color temporarily to mimic other species.

Parrotfish sleeping in a nook on a rock wall

Feeding parrotfishes 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.

Parrotfishes 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 parrotfishes 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 behavioural sex.

• 

  Female Scarus psittacus (= initial phase)

• 

  MaleScarus psittacus (= terminal phase)

Economic importance

A commercial fishery exists for some of the larger tropical species, particularly in the Indo-Pacific. Protecting parrotfishes is proposed as a way of saving Caribbean coral reefs from being overgrown with seaweed and sponges. Despite their striking colors, their feeding behavior renders them highly unsuitable for most marine aquaria.

A new study has discovered that the parrotfish is extremely important for the health of the Great Barrier Reef, it is the only one of thousands of reef fish species that regularly performs the task of scraping and cleaning inshore coral reefs.

Taxonomy

A characteristic parrotfish : Scarus globiceps (male), il Réunion island.

According to the World Register of Marine Species :

• sub-family Scarinae
  • genus Bolbometopon Smith, 1956 (1 species)
  • genus Cetoscarus Smith, 1956 (2 species)
  • genus Chlorurus Swainson, 1839 (18 species)
  • genus Hipposcarus Smith, 1956 (2 species)
  • genus Scarus Forsskål, 1775 (53 species)
• sub-family Sparisomatinae
  • genus Calotomus Gilbert, 1890 (5 species)
  • genus Cryptotomus Cope, 1870 (1 species)
  • genus Leptoscarus Swainson, 1839 (1 species)
  • genus Nicholsina Fowler, 1915 (2 species)
  • genus Sparisoma Swainson, 1839 (15 species)

• 

  Bolbometopon muricatum

• 

  Calotomus viridescens

• 

  Cetoscarus bicolor

• 

  Chlorurus sordidus

• 

  Hipposcarus longiceps

• 

  Scarus vetula

• 

  Sparisoma viride

Timeline of genera

External links

• Parrot Fish Profile from National Geographic
• Parrot Fish Care
• Parrotfish info on Fishbase