Thalassoma ballieui (Blacktail Wrasse/Old Woman Wrasse). Endemic to Hawaii, and part of an ancient lineage of Thalassoma (containing only it and it's Western Australian endemic sister species, T. septemfasciatum), diverged from the rest of the genus before the the genus invaded coral reef habitats, retaining the genus' ancestral habitat of subtropical macroalgal rocky reefs.
@Ebirah766 yes, it's quite a rare species in captivity. Perhaps this is due to a combination of its habitat (generally more subtropical reefs to the northeast of the main Hawaiian Islands), drab colouration and large size making it generally undesirable for aquariums. But is is a truly fascinating fish in an evolutionary context, a true relic of the Miocene!
