Bluehead wrasses are common to the tropical waters of the western Atlantic Ocean. Their primary range includes the region around Bermuda and the waters south of Florida, reaching to northern South America and extending west into the southeast area of the Gulf of Mexico.

Biogeographic Regions: atlantic ocean

Bluehead wrasses have long, semi-cylindrical or cigar-shaped bodies. Their scales are round and flat. They have a pointed snout, and the mouth contains teeth. Their size and color, however, depend on whether they are terminal phase males, initial phase males, or females. Terminal phase (TP) males, also known as "supermales," have blue heads and green bodies. Three stripes (black, white, and black again) divide the colors of the head and body. Terminal phase males measure about 70 to 80 mm in length while initial phase males are approximately 60 mm. Initial phase (IP) females and males are colored in two different ways. One type has a yellow upper half of the body followed by a slight green/black area and then a white lower half. Females and initial phase males are also known to be white both above and below the dark area. This type of coloration is found in fish that primarily inhabit inshore regions. A dark spot is found on the anterior dorsal fin of both types of females and initial phase males. It should also be noted that females and initial phase males have the ability to change into terminal phase males and this switch includes a change of size and coloration. In addition, once there is a transformation from female or initial phase male to terminal phase male, the change is permanent.

Range length: 80 (high) mm.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry ; polymorphic

Sexual Dimorphism: sexes colored or patterned differently

• Marine

Bluehead wrasses live in tropical waters, often around coral reefs, as well as offshore reefs. They are also known to inhabit other areas such as inshore bays and seagrass beds. Herds of bluehead wrasse that consist of initial males and females feed in reefs, rubble beds, and gorgonian fields. Bluehead wrasses inhabit areas that vary in size, the size of the area usually reflecting population size, with about 200 fish living on a small reef and up to 10,000 fish on some of the larger reefs. Tagging studies have shown that blueheads do not move from reef to reef.

Range depth: 1 to 25 m.

Habitat Regions: tropical ; saltwater or marine

Aquatic Biomes: reef

These fish forage for zooplankton, worms, mollusks, echinoderms, shrimp, and other small crustaceans at depths of 3 to 80 feet. Initial phase bluehead wrasses primarily eat zooplankton found in the water current, but herds of females and initial phase males also hunt daily during daylight hours. By hunting in packs, IP bluehead wrasses steal eggs from egg-laying fishes including redlip blennies (Ophioblennius atlanticus), bicolor damselfish (Stegastes partitus), and sergeant majors (Abudefduf vaigiensis). A herd of bluehead wrasses are able to interrupt the defenses of the nest's guardian and steal eggs for several minutes before they are driven away.

Bluehead wrasse diet also consists of parasites found on other fish. Although initial phase bluehead wrasse are one of the primary cleaners of the Caribbean, they only account for 10% of the cleaning activity on the reefs because they are also frequently preyed upon by the fish they clean. Nonetheless, bluehead wrasses remove parasites and reduce disease among fish that stop at cleaning stations. By cleaning wounds of injured fish, it is speculated that they speed up the healing process. Terminal phase males rarely function as cleaners because of their well-developed teeth which enable them to eat hard-shelled invertebrates.

Animal Foods: fish; eggs; mollusks; aquatic or marine worms; aquatic crustaceans; zooplankton

Foraging Behavior: filter-feeding

Primary Diet: carnivore (Piscivore , Eats eggs, Eats non-insect arthropods, Molluscivore , Vermivore, Scavenger ); planktivore

Bluehead wrasse are described as "one of the most successful cleaner fish" in the tropical Atlantic. They feed on the parasites of other fish that come to wrasses to be cleaned. Initial phase bluehead wrasse are classified as primary cleaners and they account for ten percent of the cleaning activities that take place within Caribbean reefs. Initial phase bluehead wrasse have also been spotted cleaning parasites from the mouths of other fish as well as purifying the wounds of injured fish.

A list of the known predators of Thalassoma bifasciatum is shown below.

Known Predators:

• Trumpetfish, Aulostomus strigosus 
• Red hind, Epinephelus guttatus 
• Yellowfin grouper, Mycteropera venenosa 
• Greater soapfish, Rypticus saponaceus 

Prior to mating, it has been observed that terminal phase males seem to communicate with females in an attempt to attract them. Terminal phase males wait in their spawning sites for females to arrive. The terminal phase males then perform signal jumps, which involve quick, vertical dashes repeated over and over. The signal jumps are a way for terminal phase males to communicate to females that they are present and ready to mate and also to show that their site is free from predators. It was also observed that a terminal phase male sometimes extends this communication, which takes place prior to mating, by descending to the female and making contact with her dorsal area.

Females, on the other hand, are not known to exhibit behaviors like the terminal phase males. A female communicates to the male that she is ready to mate by turning her head upwards and then dashing towards the surface of the water.

Terminal phase males exhibit aggressive behavior to other fish, especially just before mating. This form of communication is demonstrated when they chase other organisms from the site they pick to spawn. Initial phase males and females are not typically aggressive unless they are developing into terminal phase males. This characteristic of aggression helps distinguish social rank among the terminal phase males, initial phase males, and initial phase females with the terminal phase males being the only group to behave aggressively towards other fish.

Body color seems to be important in communication, as color communicates social status and mood during aggressive encounters (see Behavior).

Communication Channels: visual ; tactile

Perception Channels: visual

Bluehead wrasses begin in a larval state. Bluehead larva are 12 mm in length and have one large black spot at the anterior end of the dorsal fin as well as a series of small black dots along the distal edges of the dorsal, anal, and caudal fins. There are no erythrophores behind the head. The larvae spend 6 to 8 weeks in the open sea, then bury themselves in the sand as they metamorphose into juveniles. Individual fish mature at 35 mm standard length.

As the juveniles age, they turn yellow and collect in groups either in select areas of the reef or seagrass beds. The fish stay there until they completely develop and reach sexual maturity. Those that survive this stage eventually develop a dark stripe along their body. They will then become a part of a nearby population and are considered to be in the initial phase. Bluehead wrasses tend to stay where they have settled.

Development - Life Cycle: metamorphosis

The maximum lifespan is estimated to be 3 years for individuals reaching the terminal phase.

Average lifespan

Status: captivity: 3 years.

This fish species exhibits protogyny (females are capable of becoming males). Females, IP males, and TP males, however, are capable of reproducing. The density of TP males in the spawning sites is associated with the size of the reef. On small reefs (under 600 sq. m) with fewer than 200 bluehead wrasses, there are very few IP males and TP males defend territories of a small number of females. On large reefs (over 1000 sq. m) with over 400 bluehead wrasses, IP males may make up 50% of the population. Here, group-spawning is much more common particularly in downcurrent areas. In areas of high population density, TP males tend to be found primarily in upcurrent sites.

Mating System: polygynandrous (promiscuous)

Terminal phase males aggressively defend breeding sites and therefore gain exclusive access to females visiting the site. They may mate with more than 100 females per day, but the mean range is from 30 to 50.

Initial phase males exhibit no breeding site defense, are much less aggessive than TP males and often sneak-mate with a TP male/ female pair. The IP males mate in large aggregations where the operational sex-ratio can exceed 50 IP males per female.

Initial phase females have no breeding site defense, show little aggression toward other IP fish and visit spawning sites containing either single TP males or IP male aggregations.

Transitional sex changers aggressively defend their breeding sites from the first day with an increase over the next several days. They display a full repertoire of mating behavior including spawning, but do not contribute gametes until the sex change is complete, which happens within 7 to 10 days.

Breeding interval: Males breed daily, females breed every 2 to 3 days.

Key Reproductive Features: iteroparous ; year-round breeding ; sequential hermaphrodite (Protogynous ); sexual ; fertilization (External ); broadcast (group) spawning; oviparous

Bluehead wrasses provide no parental care for their offspring.

Parental Investment: no parental involvement

Bluehead wrasses are not found on any of the conservation lists.

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: least concern

There was no information found about any negative impacts Thalassoma bifasciatum may have on humans.

These fish have no economic value as a food source, because of their small size, but the brilliant colors of the bluehead wrasse make these fish popular for use in the aquarium trade. Their coloration and daily spawning make them a favorite among divers visiting the Caribbean.

Bluehead wrasses have been studied for over 70 years. This species is a popular research subject primarily because of its ability to change sex.

Positive Impacts: pet trade ; ecotourism ; research and education