#6: Our Reef Residents - bluehead wrasse

This is the first entry in a series we're going to call: "Our Reef Residents." Each entry will profile one of the species in the Giant Ocean Tank's tropical reef!

This entry is the bluehead wrasse (Thalassoma bifasciatum). Blueheads live in the tropics and are found around coral reefs and in seagrass beds. We collected several specimens (along with blackear, bluehead, dwarf, rainbow, and yellowhead wrasses) on the recent Bahamas Collecting Expedition.

Wrasses are fast swimmers and it is an exhausting process to catch them underwater. Although challenging, it is worth the extra effort to bring these beautiful fishes home to Boston and introduce them to the Giant Ocean Tank.

Wrasses belong to the Family Labridae which contains over 600 different species. Many members of this family, like the bluehead, have an interesting reproductive biology. Blueheads are typically born female. Males are produced when a female sexually reverses after a dominant male is predated upon or dies. This process is called protogyny. The "supermale" wrasse maintains reproductive control over a smaller group of females, or harem, while also keeping geographical control over a certain area. The male has striking coloration and is referred to as a terminal phase male.

Females are less brightly colored and are called initial phase wrasses. Occasionally, a bluehead will be born male; it is also considered an initial phase wrasse. These smaller males will never become dominant and will not change sex. They are also called "sneaker" or "streaker" males because they quickly move into a supermale's territory to mate with his females. This helps to ensure a high level of genetic diversity. Blueheads are pelagic spawners and release eggs into the water column for dispersal by ocean currents.

The illustration above shows both the terminal phase and initial phase of the bluehead wrasse. The terminal phase bluehead has a bright blue head, two vertical black bars separated by a white bar, and yellowish-green body. It can grow up to six inches long. The initial phase bluehead pictured is a juvenile and has a yellow back, white underside, and black spot on its dorsal fin. The appearance of initial phase blueheads varies depending on the age of the wrasse and its geographic location. They range from one to four inches in length. Both the terminal phase and initial phase blueheads reside in the Giant Ocean Tank here at the New England Aquarium.



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