Marine Animal Encyclopedia
Bluehead Wrasse Thalassoma bifasciatum
Species ID: L.TB
Description: A small cigar-shaped fish that swims by beating its pectoral fins. There are three primary colour phases for adults that reflect their age and development – initial, intermediate and terminal phases. The initial phase (a) is characterized by a yellow back and a white belly, often with a dark stripe running along the boundary between these colours. The terminal phase male (b) (also known as the supermale) has a yellow to green body with a bright blue head. Just behind the head is a series of thick bars – black, white, and black again – unique to this species. The juvenile phase resembles the initial phase but is smaller, and may be completely yellow to white depending on location
Maximum Size: 25 cm (10 in)
Longevity: 3 years
Status: Not currently on the IUCN endangered species list
Bluehead Wrasse & People: Not caught for consumption in the Caribbean, but often used as a bait fish or collected on a small scale for the aquarium industry
Geographical Range: This fish is incredibly abundant on shallow coral reefs throughout the Caribbean and Gulf of Mexico, north to the Carolinas and south to Brazil
Coral Reef Zone: Found in all coral reef zones, but less common in the drop-off zone
Favourite Habitat: The bluehead wrasse can be found in all types of coral reef habitat, as well as mangrove areas and seagrass beds
Depth Range: 0–40 m (0–131 ft)
A Day in the Life:
Dawn: Bluehead wrasses emerge from their night shelters and begin their search for food
Day: These fish move in large feeding groups across the reef. Spawning may also occur after midday
Dusk: Activity decreases as individuals find shelter for the night
Who Eats Who
Bluehead wrasses are carnivores, feeding mainly on zooplankton and small benthic organisms, like shrimps and worms, although they also consume the eggs of other small fish. Initial phase bluehead wrasses sometimes operate as cleaners, eating the parasites of other marine organisms. These fish are consumed most commonly by trumpetfish and grouper.
Scuba Diver & Snorkeler Best Practices
Remove only recent garbage from the sea : Garbage that has been in the sea for a long time might have been adopted as a new home by some marine organisms; encrusting organisms may also call it home. Remove only recent garbage from the sea.
Bluehead wrasses are unafraid and very easy to approach. During the day, large schools of initial phase bluehead wrasses may be encountered on the reef, but they hide within the reef at night.
Bluehead wrasses are carnivores that hunt actively for food during the day, and can change their feeding strategy according to the reef conditions. If currents are strong, they are found above the reef, feeding on zooplankton – tiny animals that float in the oceans’ currents. When currents are weak, bluehead wrasses search the reef for bottom-dwelling animals, such as crabs, shrimps and worms. Their favourite foods are the fatty, nutritious eggs of other fishes. Nest defenders, such as damselfishes, can be completely overwhelmed by the large schools of bluehead wrasse that take advantage of the chaos they create in order to raid the nests for eggs. Juvenile bluehead wrasses may also act as cleaners – removing the parasites from other reef creatures.
Observe, record & share:
O L.TB-101 – Zooplankton feeding: When currents are strong, bluehead wrasses feed on zooplankton above the reef
O L.TB-102 – Bottom feeding: When currents are weak, bluehead wrasses search for benthic (bottom-dwelling) animals
O L.TB-103 – Egg feeding: Nest-guarding fish are overwhelmed by schools of bluehead wrasse
O L.TB-104 – Juvenile cleaners: Juvenile bluehead wrasses may clean parasites from other reef creatures
Attack & Defense Behaviour
Bluehead wrasses do not defend territories, and initial phase fish usually move across the reef in large feeding schools, which offer them some protection from predators. Juvenile bluehead wrasses are protected to a certain degree by their pale colour, which helps camouflage them against a sandy backdrop. Juveniles have also been observed hiding within the tentacles of anemones when threatened, even though they themselves are vulnerable to the anemones’ stinging nematocyst cells. In contrast, the older, terminal phase bluehead wrasse spend most of their time alone while patrolling spawning sites that are usually located at the end of reef spurs.
Observe, record & share:
O L.TB-201 – Schooling: Initial phase bluehead wrasses school when threatened
O L.TB-202 – Hiding in anemones: Juvenile bluehead wrasses hide within the tentacles of anemones when threatened
O L.TB-203 – Solitary terminal males: Terminal phase bluehead wrasses are loners, patrolling spawning sites at the end of reefs
Bluehead wrasse spawning strategies are complex. The species is a protogynous hermaphrodite, which means individuals change sex from female to male as they grow and age. The initial colour phase includes both males and females, whereas the larger and rarer terminal colour phase is exclusively male. Bluehead wrasses may practice pair spawning or group spawning. During pair spawning, terminal phase males signal their intent to mate by swimming vertical loops known as “signal jumps”, or by bending the body and raising the dorsal fin as they swim by females. Later in the day, initial phase females seek out terminal phase males at their spawning sites, often located at the edge of the coral reef. Males swim laps or circular patterns above the female to indicate their readiness to spawn, and if the female is interested, the two fish rush towards the surface together, intertwine and release a cloud of eggs and sperm into the water. During group spawning, a school of initial phase fish roughly 50 strong forms prior to spawning and small groups of 5-10 fish, called “spawning balls”, periodically break off from the main group and rush towards the surface to release eggs and sperm together. Spawning in this species takes place year round, during a two hour window in the afternoon.
Observe, record & share:
O L.TB-301 – Signal jumps: Terminal phase males swim in long vertical loops to attract females
O L.TB-302 – Courtship display: Terminal phase males bend their body towards females and raise their dorsal fin, indicating their desire to mate
O L.TB-303 – Swimming laps: Terminal phase males swim short laps above the female they wish to spawn with
O L.TB-304 – Pair spawning: Spawning pairs rush towards the surface and release gametes
O L.TB-305 – Spawning group: Initial phase fish (both males and females) gather in large groups
O L.TB-306 – Spawning ball: A small group of initial phase fish rushes upwards to spawn
Pair Spawning: Pair spawning between terminal males and initial phase females is a common and well-documented behaviour on Caribbean coral reefs. The female arrives at the spawning site patrolled by the male and approaches him from below. The male swims short laps back and forth or swims circles above the female, quivering his tail to entice her. Abruptly, the two fish rush together towards the surface, with the female leading the way. Both fish intertwine so that their genitals align, with the female almost upside down, and together release a cloud of eggs and sperm. After spawning, both fish return to the reef where males resume courtship with other females.
Did You Know?
• Bluehead wrasses can change from male to female in only a few days, and the trigger that prompts sex change is often a shift in community structure. For example, when a terminal phase male is lost, the largest and highest ranking initial phase female changes into a new terminal phase male.
• A single energetic male can spawn as many as 15 times in a 30 minute period with different females.
What to do?
Share your observations today!: Discover your species of interest, observe its behaviour, and share your pictures and videos with friends and coral reef enthusiasts around the world! Upload media to the web, tagged with species common name (ex.: trumpetfish) and species ID code (ex.: A.AM) or species behaviour code (ex.: A.AM-101)