[5] 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.

[1][7] A significant parasite of T. bifasciatum is the intracellular myxozoan Kudoa ovivora, which can be found in the ovaries of females.

[8] Infected bluehead wrasses have been found to change sex earlier than uninfected females, possibly in response to the parasite.

[9] 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.

However, this species shows high site fidelity, so coral reef destruction could cause local endangerment.

This enables the initial phase males to produce more sperm for the snatched opportunities they must take when trying to fertilize the eggs of the females in the guarded harem.

These groups consist of 20–50 or more IP males that congregate at specific sites during the daily spawning period on medium and larger sized reefs.

Thalassoma bifasciatum and its congener, the saddle wrasse (T. duperrey) have become important models for understanding the physiological and neurobiological bases of sex change.

[3][12][14] Sex change has been studied in bluehead wrasses primarily using field manipulations, where it can be induced in large females by removing dominant terminal phase males from small reefs.

Gonadotropin-releasing hormone (GnRH) neurons differ across sexual phenotypes in the hypothalamus of bluehead wrasses and also with androgen implants that induce sex change.

Behavioral sex change occurs even in females whose gonads (ovaries) have been surgically removed prior to becoming socially dominant.

Large terminal phase males will defend breeding sites to which females migrate on a daily basis.

All terminal phase males or all females were replaced in local isolated populations, and the resulting site use was monitored.

[5] Most of the literature on mating systems of the blue-headed wrasse was described in small patches of concentrated reef habitats.

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.