Black hamlet
(Hypoplectrus nigricans)

Hypoplectrus nigricans, the black hamlet, is native to shallow parts of the central Western Atlantic Ocean and Caribbean Sea.

It grows to about 15 cm (6 in) in total length.

It is a simultaneous hermaphrodite, with a breeding strategy known as egg trading. One fish acts as a female and lays a batch of eggs which the other fertilises. The following night, the roles are reversed.

Hypoplectrus nigricans is a small fish growing to a total length of 85 to 150 mm (3.3 to 5.9 in). The morphology and colouring of the fish varies across its range. Fish from Puerto Rico have greyish bodies, translucent pectoral fins, pointed pelvic fins and a caudal fin shaped like a crescent moon. Fish from Mexico and Belize are slightly smaller and have a darker body colour with dark pectoral fins, blunt pelvic fins and a short, square-cut caudal fin.

The species is native to the central West Atlantic Ocean. Its range extends from southeastern Florida and the Bahamas, through the Caribbean Sea and the Gulf of Mexico to Santa Marta in Colombia and to the islands off the coast of Venezuela. It is a reef fish, inhabiting reefs with both stony corals and soft corals.