BLUEHEAD WRASSE: PRIVATE LIFE LAID BARE
The bluehead wrasse (or blue-headed wrasse) Thalassoma bifasciatum is a denizen of the coral reefs of the tropical waters of the western Atlantic Ocean. This bright little 4-inch fish is… a wrasse with a blue head. No more and no less. Unless it’s a juvenile. Then it is mainly bright yellow. It’s similar to BLUE TANG (aka ‘the Disney Dory’), which starts life bright yellow and grows up to be blue.
The species may be found singly, in pairs or small groups, or in schools. They have an important role to play in the life of the reef. They are CLEANER FISH, vital to the health and wellbeing of the larger species they attend to, and thus of the reef itself. This is ‘cleaning symbiosis’, a relationship of mutual benefit. The big fish get cleaned; the little fish have a useful function and – importantly for them – therefore don’t get eaten.
Having said that, blueheads are of course fair game as a snack for species that aren’t in the market for their cleaning services. And, unfairly, some species that are content to let cleaner gobies runtle around their gills and mouths are not so considerate of the wrasse. Some types of grouper and moray eel, for example.
TELL US EXACTLY SEVEN BLUEHEAD WRASSE FACTS
- Juveniles can alter the intensity of their colour, stripes & bars
- The bluehead wrasse is a ‘protogynous sequential hermaphrodite’
- All are born female**. Some change sex to male during maturation (see below)
- Food includes zooplankton, small molluscs and small crustaceans…
- …and parasites / other juicy bits (fungal growths, anyone?) from bigger fish
- The main threat to the species is coral reef degradation or destruction
- The bright colours invite aquarium use, but the trade is not a significant one
** Some sources suggest some are born male and remain male. I’m not sure which is right
A juvenile bluehead (with feather-duster worms) – mostly yellow, with a pale underside
THE REMARKABLE SEX LIFE OF THE BLUEHEAD WRASSE
This is an unavoidable topic, I’m afraid. The bluehead’s sex life is the most interesting thing about them, and this is no time to be prudish. It is the subject of extensive scientific research, not all of which I have read since I decided to write about the species last night. Like many human relationships, “it’s complicated”, but in a conch shell it boils down to this:
- To recap, BWs are born female and as they mature, some become male.
- Males reach an ‘initial phase’ when they can breed in groups with females
- Some males grow even larger & reach full colouration. This is the ‘terminal phase’
- These large males aggressively chase away smaller ones & seek females to pair with
- Their state of readiness (as it were) is signalled by colour changes
- This behaviour is similar to that seen in many city centres in a Saturday night
- The smaller fish have one bonus – their sperm count is higher than a dominant male
- Prozac tests have shown that the drug reduces a dominant male’s aggression
As the excellent organisation OCEANA puts it: Bluehead Wrasses may reproduce in four different ways throughout their lifetime: 1) as a female in a group spawning event; 2) as a female in a pair spawning event within the territory of a large male; 3) as a small male in a group spawning event; and 4) as a dominant, terminal male in a pair spawning event within its own territory.
A cropped still from a video I took at Fowl Cay marine reserve. I’ve looked at dozens of images online and not found one that was all blue with a yellow end to its tail fin. Maybe it’s not a BW at all. Or it’s a different type of fish completely. Or perhaps it is just an all-blue alpha male.
Credits & Sources: Melinda Riger; Adam Rees; James St John; Oregon State edu / Pinterest; Wiki images; self; Oceana; IUCN; magpie pickings
A bluehead wrasse passes the time of day with a grunt