Black Hamlet

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.

As a simultaneous hermaphrodite, H. nigricans has an unusual reproductive strategy known as egg trading. The fish is usually solitary, but at breeding time two fish come together at night. Courtship is initiated by one fish which temporarily takes a female role. The other fish acts as the male and fertilises a batch of eggs produced by the first fish. The following night their roles are reversed, and the second fish lays eggs and the first fish fertilises them. The two fish continue alternating roles in this way over the course of several nights. The pair usually stay together for the series of transfers, but sometimes each finds a different partner.