Blue hamlet (Hypoplectrus gemma)

Classification (WoRMS)

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

Accepted name: Hypoplectrus gemma · Authority: Goode & Bean, 1882 · Taxonomic status: accepted · AphiaID: 281114.

Source: World Register of Marine Species (WoRMS) — https://www.marinespecies.org/aphia.php?p=taxdetails&id=281114 (CC BY 4.0). Accessed 2026-09-23.

Biology and life history (FishBase)

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

Maximum length: 13 cm · Habitat zone: reef-associated · Body shape: fusiform / normal · Vulnerability index: 10 of 100 · Fishery importance: commercial · Aquarium trade: never/rarely.

Source: FishBase species summary (SpecCode 47813) — https://www.fishbase.se/summary/Hypoplectrus-gemma.html (CC BY-NC 3.0 — non-commercial use only). Accessed 2026-09-23.

Distribution and occurrence records (GBIF)

21,573 georeferenced occurrence records for Hypoplectrus gemma are published through GBIF from 4 countries or marine areas. The map above plots 23 distinct locations from a sample of 3,000 records, omitting 2 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 (21,111); Puerto Rico (443); Belize (15); Virgin Islands (U.S.) (4).

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

Source: GBIF Occurrence Search (taxonKey 2388766) — https://www.gbif.org/occurrence/search?taxon_key=2388766&has_coordinate=true (records CC0 / CC BY); WoRMS distribution records (MarineRegions) — https://www.marinespecies.org/aphia.php?p=taxdetails&id=281114 (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 gemma Goode & Bean, 1882 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 190290) — https://www.iucnredlist.org/species/190290/0; GBIF IUCN Red List category endpoint (taxonKey 2388766) — https://api.gbif.org/v1/species/2388766/iucnRedListCategory. Accessed 2026-09-23.

Description and natural history (Wikipedia)

Hypoplectrus gemma has a deep body which is markedly compressed laterally. It has a straight forehead and a rather short snout which has a protrusible top jaw The preoperculum is angular and has serrations along its edges and a number of small spines which point to the head on its lower edge close to the angle. The dorsal fin has ten spines and 14-17 soft rays and is continuous. It has long pelvic fins which extend as far as, or beyond the anus. The caudal fin is slightly forked. The head, body and fins of this species are plain iridescent blue and there is a black stripe on the upper and lower edges of the caudal fin. This species has a maximum recorded length of 13 cm, although the method of fish measurement used was not given.

Hypoplectrus gemma is found in the western Atlantic Ocean. It was considered to be endemic to Florida but it has since been discovered off the Yucatan Peninsula in Mexico, It has also been found in the Dutch West Indies off the island of Bonaire. It has also been recorded on the northern Bahamas and in Cuba.

Hypoplectrus gemma is found on shallow reefs, at depths of 3 to 20 m. The species in the genus Hypoplectrus are synchronous hermaphrodites and they have the ability to move between "male" and "female" roles when spawning. The colour pattern of this species resembles that of the blue chromis (Chromis cyanea) and it has been suggested that the blue hamlet mimics the blue chromis. 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. The purpose of this mimicry may be to allow H. gemma to prey on the young of the blue chromis but this has yet to be proven. This is a carnivorous species which feeds on other fishes and non-sessile benthic crustaceans.

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.

Hypoplectrus gemma is used in the aquarium trade but whether it is rare or common in that trade is unclear.

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