About Hypoplectrus unicolor (Walbaum, 1792)
Hypoplectrus unicolor has a deep, highly laterally compressed body and head, with a straight forehead, rather short snout, and a protrusible upper jaw. Its preoperculum is angular, with serrations along its edge, and a number of small forward-pointing spines on its lower margin near the angle. The continuous dorsal fin has ten spines and 14 to 17 soft rays. It has long pelvic fins that extend to or beyond the anus, and the caudal fin is slightly forked. The body ranges in color from greyish white to yellow, with a darker back, and a large black saddle-like marking on the caudal fin base that extends over the lateral line on each side. Horizontal iridescent blue lines run along the head, and occasionally extend as far as the front edge of the pelvic fins. There is a distinct blue line around the eye, and some individuals may have two black spots on the snout. The pelvic fins are yellowish, while the pectoral fins are transparent. This species reaches a maximum total length of 12.7 centimetres (5.0 in). Hypoplectrus unicolor is distributed in the western Atlantic, ranging from Cape Canaveral in Florida south to the Bahamas, into the Gulf of Mexico as far west as Cedar Key, along the mainland coast of Mexico from Tuxpan to the northern Yucatan Peninsula, and from northwestern Cuba south through the Caribbean Sea. This species occurs on shallow fringing reef faces, the front slopes of reefs, and under piers. It is normally found at depths between 3 and 25 metres (9.8 and 82.0 ft). It is a carnivorous species whose diet consists mainly of crustaceans and smaller fishes. Juveniles are frequently found in mangroves. Species in the genus Hypoplectrus are synchronous hermaphrodites, and can switch between "male" and "female" roles when spawning. It has been proposed that H. unicolor is a mimic of the foureye butterflyfish (Chaetodon capistratus); this suggestion is based on similarities in color pattern, general body shape, shared use of similar shallow water habitats, the comparative scarcity of H. unicolor, and their differing prey preferences: H. unicolor feeds on mobile benthic animals, while C. capistratus feeds on sessile benthic invertebrates. However, H. unicolor varies in color and pattern across its geographic range, while C. capistratus does not, and the juveniles of the two species do not resemble each other. Even so, there is an association between the two: H. unicolor individuals that follow feeding pairs of C. capistratus have higher prey capture success than hamlets that do not associate with butterflyfish.
