Bluehead facts for kids
Quick facts for kids Bluehead |
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Thalassoma bifasciatum, the bluehead, bluehead wrasse or blue-headed wrasse, is a species of marine ray-finned fish, a wrasse from the family Labridae. It is native to the coral reefs of the tropical waters of the western Atlantic Ocean. Individuals are small (less than 110 mm standard length) and rarely live longer than two years. They form large schools over the reef and are important cleaner fish in the reefs they inhabit.
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Distribution and habitat
Thalassoma bifasciatum is found in coral reefs of the Atlantic Ocean. Its main range includes the Caribbean Sea and the southeast area of the Gulf of Mexico.
Description
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Young/small females and males have yellow upper bodies and white lower bodies, often with green or black lateral stripes and occasionally dark vertical bars. This coloration is known as the initial phase. They can rapidly alter the presence or intensity of their yellow color, stripes, and bars, and these color changes appear to correspond to behavioral changes. Large females and some males can permanently change coloration and/or sex and enter the terminal phase coloration, which has a blue head, black and white bars behind the head, and a green body. This color phase gives the species its name. Terminal phase males are larger (70 to 80 mm) than the initial phase males (60 mm).
Ecology
Diet
Thalassoma bifasciatum forages for zooplankton, mollusks, small crustaceans (such as shrimp and krill), worms, other motile invertebrates, and the eggs of smaller fish, as well as ectoparasites on other fish. Initial phase males eat primarily zooplankton from currents, and females and initial phase males have certain hunting times during the day.
Predators and parasites
Though Thalassoma bifasciatum is a common cleaner fish in the coral reefs they inhabit, they avoid cleaning piscivores such as the spotted moray, the graysby, and the red hind. Such species will view them as prey, but will not view gobies, another kind of cleaner fish, as prey. Other predators include the greater soapfish, roughtail stingray, and the trumpetfish.
A significant parasite of T. bifasciatum is the intracellular myxozoan Kudoa ovivora, which can be found in the ovaries of females. Infected eggs are sterile and are also larger than uninfected eggs, and contain more organic and inorganic material. This implies the parasite causes a shift in resources from the mother to the eggs and decreases the fitness of the mother. Infected bluehead wrasses have been found to change sex earlier than uninfected females, possibly in response to the parasite.
Conservation status
Thalassoma bifasciatum is widespread in the northwestern Atlantic region and is one of the most abundant species in coral reefs near Puerto Rico, the Virgin Islands, and the Netherlands Antilles. It is listed under Least Concern. However, this species shows high site fidelity, so coral reef destruction could cause local endangerment. Due to its bright coloration, it is sometimes collected for the aquarium trade, but this is not a threat to the species.
Behavior
Like many other wrasse species, Thalassoma bifasciatum is a protogynous sequential hermaphrodite; individuals may begin life either as males or females, but females can change sex later in life and become males.
Social system
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A specific social system exists within the males - terminal phase males (which are the most aggressive and have the "highest" ranking among the males) and initial phase males (which mate when they can get a chance in a larger group). Color change of the T. bifasciatum indicates their motive or role. When terminal phase males chase initial phase males, their color changes to a metallic green, whereas when they are courting a female, they become pink/grey and form black circles on their fins.
Sex change
Initial phase females and initial phase males both can change into terminal phase males. This change can be relative quick, taking around 8 days. However, this change in sex is permanent: once an initial phase female or male changes into a terminal phase male, it cannot change back.
Mating systems
Large terminal phase males will defend breeding sites to which females migrate on a daily basis. A study was done to estimate the relative roles of each sex in choosing the location of such sites. All terminal phase males or all females were replaced in local isolated populations, and the resulting site use was monitored. After males were replaced, the mating system was not affected. On the other hand, after the females were replaced, half of the old sites were lost and the same number of new sites came into use, and continued to be occupied for over a year after these manipulations. This occurred although large males originally continued to defend and display at the original sites. Therefore, this shows the importance of female choice in the feeding system of the blue-headed wrasse, and that males will respond to the females' site preferences.
T. bifasciatum do not have distinct territories and their populations roam freely. Also, the females usually do not leave their original spawning spots. The males are known be taken away or leave. A plausible reason for why the females stay could be that they are most accustomed to those areas, and also because the predator threat is constant. Most of the literature on mating systems of the blue-headed wrasse was described in small patches of concentrated reef habitats. In a large, linear barrier reef in St. Croix, U.S. Virgin Islands, very large aggregations of group-matings form daily in a single area near the foreside of the reef. Tagging studies have shown that fish are generally faithful to particular feeding schools that are assorted throughout the forereef, and that they tend to migrate to spawning grounds over 1.5 kilometers away. There is no mating that appears to happen in other upcurrent areas of the forereef. Despite large differences in the times that are spent on the migration, there are no significant differences in the fecundity or frequency of spawning among females that live at different distances from the mating aggregation. The higher growth rate corresponded to a higher general feeding rate in the location, suggesting that food intake may outweigh the costs of the long migration.
