Butter hamlet (Hypoplectrus unicolor)

Classification (WoRMS)

Full classification as recorded by WoRMS: Kingdom: Animalia · Phylum: Chordata · Class: Teleostei · Order: Perciformes · Family: Serranidae · Genus: Hypoplectrus.

Accepted name: Hypoplectrus unicolor · Authority: (Walbaum, 1792) · Taxonomic status: accepted · AphiaID: 281121.

Synonyms and superseded combinations recorded for this taxon: Hypoplectus unicolor (Walbaum, 1792); Perca unicolor Walbaum, 1792.

Source: World Register of Marine Species (WoRMS) — https://www.marinespecies.org/aphia.php?p=taxdetails&id=281121 (CC BY 4.0). Accessed 2026-09-23.

Biology and life history (FishBase)

Measured values published by FishBase for Hypoplectrus unicolor. Only fields the database actually holds for this species are shown; these are database values, not aquarium guidance.

Maximum length: 12.699999809265137 cm · Habitat zone: reef-associated · Body shape: short and / or deep · Vulnerability index: 10 of 100 · Fishery importance: commercial · Aquarium trade: commercial.

FishBase notes: Mainly carnivorous (Ref. 13810). Has been reared in captivity (Ref. 35420).

Source: FishBase species summary (SpecCode 3329) — https://www.fishbase.se/summary/Hypoplectrus-unicolor.html (CC BY-NC 3.0 — non-commercial use only). Accessed 2026-09-23.

Distribution and occurrence records (GBIF)

32,077 georeferenced occurrence records for Hypoplectrus unicolor are published through GBIF from 37 countries or marine areas. The map above plots 77 distinct locations from a sample of 3,000 records, omitting 12 inland records that carry an institution's coordinates rather than a collection site; it shows where the species has been observed and reported, not a modelled range.

Most records by country or area: United States of America (28,391); Puerto Rico (2,461); Virgin Islands (U.S.) (608); Bonaire, Sint Eustatius and Saba (83); Belize (65).

The full country table, WoRMS marine regions and the sampling notes are on this species' Distribution page.

Source: GBIF Occurrence Search (taxonKey 2388770) — https://www.gbif.org/occurrence/search?taxon_key=2388770&has_coordinate=true (records CC0 / CC BY); WoRMS distribution records (MarineRegions) — https://www.marinespecies.org/aphia.php?p=taxdetails&id=281121 (CC BY 4.0); Natural Earth 110m basemap — https://www.naturalearthdata.com/ (public domain). Accessed 2026-09-23.

Conservation status (IUCN Red List)

The IUCN Red List assesses Hypoplectrus unicolor (Walbaum, 1792) as Least Concern (code LC). No trend, population estimate or threat analysis is given here, because none is available from this source without the Red List API; follow the source link for the full assessment, including its date.

Source: IUCN Red List of Threatened Species (taxon 16759144) — https://www.iucnredlist.org/species/16759144/0; GBIF IUCN Red List category endpoint (taxonKey 2388770) — https://api.gbif.org/v1/species/2388770/iucnRedListCategory. Accessed 2026-09-23.

Description and natural history (Wikipedia)

Hypoplectrus unicolor was first formally described in 1792 as Perca unicolor by the German physician, naturalist and taxonomist Johann Julius Walbaum (1724–1799) with no type locality given.

Hypplectrus unicolor has a deep body and head which is highly laterally compressed with a straight forehead and a rather short snout and a protrusible upper jaw. It has an angular preoperculum which has serrations on its edge and a number of small forward pointing spines on its lower margin close to the angle. The continuous dorsal fin has ten spines and 14-17 soft rays. It has long pelvic fins which extend as far as or beyond the anus. The caudal fin is slightly forked. The body is greyish white to yellow in colour with the back being darker, with a sizeable black saddle-like marking on the base of the caudal fin, this extends over the lateral line on each side. Horizontal, iridescent blue lines run along the head, occasionally these extend as far as front edge of the pelvic fins. There is an obvious blue line around the eye. Some individuals may show two black spots on the snout. The pelvic fins are yellowish in colour while the pectoral fins are transparent. This species attains a maximum total length of 12.7 cm.

Hypoplectrus unicolor is found in the western Atlantic. It extends from Cape Canaveral in Florida south to the Bahamas and into the Gulf of Mexico as far west as Cedar Key and along the mainland coast of Mexico from Tuxpan to the northern Yucatan Peninsula and from northwestern Cuba south through the Caribbean Sea.

Hypoplectrus unicolor is found on shallow fringing reef faces, the front slopes of reefs, and under piers. It is normally found at depths between 3 and 25 m>It is a carnivorous species which has a diet largely consisting of crustaceans and smaller fishes. The juveniles are frequently observed in mangroves. The species in the genus Hypoplectrus are synchronous hermaphrodites and they have the ability to move between "male" and "female" roles when spawning.

It has been suggested that H. unicolor is a mimic of the foureye butterflyfish (Chaetodon capistratus) and this proposition was based on resemblances in their colour patterns and general shape, their shared use of similar habitats in shallow waters and the comparative scarcity of H. unicolor and their prey preferences, H. unicolor feeds on mobile benthic animals while C. capistratus preys on sessile benthic invertebrates. However, H. unicolor varies in colour and pattern geographically whereas C. capistratus does not and their juveniles do not resemble each other either. There is a relationship between the two however, as individuals which follow feeding pairs of the butterflyfish have a higher success rate in capturing prey than hamlets that do not associate with butterflyfish.

Hypoplectrus unicolor is occasionally found in the aquarium trade, although it is one of the most highly desired species of hamlet in that trade. It has been reared in captivity.

Source: Wikipedia: Hypoplectrus unicolor — https://en.wikipedia.org/wiki/Hypoplectrus_unicolor (CC BY-SA 4.0). Accessed 2026-09-23.