Hypoplectrus gemma, the blue hamlet, is a species of marine ray-finned fish, a sea bass from the subfamily Serraninae which is part of the family Serranidae, which also includes the groupers and anthias.

It was considered to be endemic to Florida but it has since been discovered off the Yucatan Peninsula in Mexico,[5] It has also been found in the Dutch West Indies off the island of Bonaire.

The species in the genus Hypoplectrus are synchronous hermaphrodites and they have the ability to move between "male" and "female" roles when spawning.

The resemblance between the two species is enhanced by the more elongate body shape and deeply forked tail of H. gemma compared to its congeners.

[2] Hypoplectrus gemma was first formally described in 1882 by the American ichthyologists George Brown Goode (1851-1896) and Tarleton Hoffman Bean (1846-1916) with the type locality given as Garden Key in the Dry Tortugas of Florida.