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. (Deloach, 1999; "Bluehead wrasse", 2001; Agbayani, 2003)
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. (Deloach, 1999; "Bluehead wrasse", 2001; Warner and Swearer, 1991)
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. (Agbayani, 2003; "Bluehead wrasse", 2001; Warner and Swearer, 1991)
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. ("Larval Fish: Labroidei", 2002; Warner and Swearer, 1991)
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. (Deloach, 1999)
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. (Warner, 1984)
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. (Ford, et al., 1999; Warner and Swearer, 1991)
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. (Ford, et al., 1999; Warner and Swearer, 1991)
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. (Ford, et al., 1999; Warner and Swearer, 1991)
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. (Ford, et al., 1999; Warner and Swearer, 1991)
Bluehead wrasses provide no parental care for their offspring.
The maximum lifespan is estimated to be 3 years for individuals reaching the terminal phase. (Warner, 1998)
Bluehead wrasses exist in populations that roam freely. They have no distinct home ranges; their territories seem to overlap with one another. Females do not seem to stray from their original sites of spawning even when terminal phase males leave or are taken away. New males quickly replace the previous ones in the spawning sites, but their previous partners to not follow. It could be possible that females prefer to stay in areas they are used to, especially since the threat of predators is constant. It has also been speculated that movement to different spawning sites is a behavior that is learned. (Deloach, 1999)
A social system exists among the three different kinds of bluehead wrasses. Terminal phase males exhibit the most aggression and rank above initial phase males. Initial phase males only get to mate as sneaker males or in groups within large populations. TP males change color to indicate courtship and aggression. When chasing IP males, they become a bright, metallic green. When courting females, they become a pink-grey opalescent and develop distictive black circles on the pectoral fins. The color changes occur within a few seconds. (Dawkins and Guilford, 1993)
A unique characteristic of Thalassoma bifasciatum is the ability of these fish to change sex. Initial phase males and initial phase females are able to change into terminal phase males. This change involves a change in color, size, and functioning gonads (in the case of the females changing to males). This process of sex change is not reversible. Once an initial phase fish becomes a terminal phase male, they remain that way for life. A good deal of research has been done on these fish in order to further explore their ability to transform. Some research has been conducted by removing terminal phase males from a certain population. Results show that females do in fact make the change into males in the course of just a few days. As their body color and size change into that of a terminal phase male, they become more aggressive. Researchers are beginning to identify this change as a response to the social environment (the removal or absence of terminal phase males), which may then be related to the neuropeptide arginine vasotocin (AVT). It has been suggested that AVT is involved in the process of gonadal hormones altering behavior. (Ford, et al., 1999; Godwin, et al., 2000; Warner and Swearer, 1991)
Bluehead wrasses are able to swim with fins alone using a rowing or flapping action of the pectoral fins. This provides precise swimming movements that are useful when moving among coral reefs. The term "labriform swimming" comes from the wrasses (family Labridae) swimming behavior. (Moyle and Cech, 2000)
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. (Deloach, 1999; Warner and Swearer, 1991)
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. (Warner and Swearer, 1991)
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. (Deloach, 1999; Ford, et al., 1999)
Body color seems to be important in communication, as color communicates social status and mood during aggressive encounters (see Behavior).
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 saxatilis). 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. (Agbayani, 2003; Deloach, 1999)
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. (Deloach, 1999)
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. (Deloach, 1999)
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. (Deloach, 1999)
There was no information found about any negative impacts Thalassoma bifasciatum may have on humans.
Bluehead wrasses are not found on any of the conservation lists.
We would like to acknowledge John Godwin and Robert Warner and thank them for their help during our research of bluehead wrasses, Thalasoma bifasciatum. We would also like to extend a thank you to the 2002 class of Animal Behavior at Niagara University for their contribution to the information provided on this website: Michele DeSimone, Kyle Hull, Heidi Schulik, Tanya Poeller, Nevia Ramos, and Kevin Swartout
Liz Estoff (author), Niagara University, Donna Thompson (editor), Niagara University.
the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
uses smells or other chemicals to communicate
ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates
humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
fertilization takes place outside the female's body
union of egg and spermatozoan
a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales.
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.
eats mollusks, members of Phylum Mollusca
having the capacity to move from one place to another.
specialized for swimming
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
the business of buying and selling animals for people to keep in their homes as pets.
an animal that mainly eats fish
an animal that mainly eats plankton
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.
condition of hermaphroditic animals (and plants) in which the female organs and their products appear before the male organs and their products
structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.
mainly lives in oceans, seas, or other bodies of salt water.
an animal that mainly eats dead animals
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
uses touch to communicate
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
uses sight to communicate
breeding takes place throughout the year
animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)
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Moyle, P., J. Cech. 2000. Fishes: An Introduction to Ichthyology (4th Edition). Up Saddle River, NJ: Prentice Hall.
Warner, R. R. 1984. Mating behavior and hermaphroditism in coral reef fishes. American Scientist, 72: 128-136.
Warner, R. R. 1998. The role of extreme iteroparity and risk avoidance in the evolution of mating systems. Journal of Fish Biology, 53: 82-93.
Warner, R. R., S. E. Swearer. 1991. Social control of sex change in the Blueheaded Wrasse, Thalassoma bifasciatum (Pisces: Labridae). Biological Bulletin, 181: 199-204.