Abudefduf concolor
Uncommon damselfish of the Central Pacific: spot it around Costa Rica's Guanacaste and the Galápagos in warm 23-29C water, year-round.
A stocky little damselfish about 13 cm long, dusky grey to brownish overall with faint, often barely visible vertical bars running down its sides. Its body shape is the classic sergeant profile: deep, oval, and slightly compressed, with a small mouth built for picking at algae and invertebrates on rock. In the water it reads as a plain dark fish rather than the bright yellow-and-black striped look divers associate with other sergeants, which is the main clue to separating it from its relatives.
Expect to find it hovering close to rock and reef structure, picking over algae mats and grazing whatever invertebrates it can pry loose, rather than roaming open water. It tends to hold its ground near a patch of reef instead of bolting when divers approach, though it is rarely bold enough to come in close. Most sightings are on daytime dives over rocky or mixed rock-and-coral bottoms typical of the Eastern Pacific.
Like other sergeants, it likely guards a patch of eggs laid on rock or dead coral, with the guarding fish turning noticeably more territorial and aggressive toward anything that lingers near the nest.
No clear seasonal pattern shows up in the sighting data, and its temperature niche of 22.9 to 29.1C spans the normal range for both Costa Rica and the Galápagos year-round, so any month is fair game. Water temperature and visibility swings tied to upwelling in the Galápagos may affect your odds more than the calendar does.
Reef neighbours a diver could mistake it for. Use the identification notes above to tell them apart.
Most reliably logged along Costa Rica's Central Pacific and Guanacaste coasts, with a second strong population around Ecuador's Galápagos Islands and Pacific coast. Costa Rica edges out Ecuador as the more frequent country for sightings, though at both it tends to be an uncommon rather than everyday find.
Mapping where Dusky Seargent is logged…
Best chances are along Costa Rica's Central Pacific and Guanacaste coasts, plus Ecuador's Galápagos Islands and Pacific coast. It shows up at dozens of sites across these two countries but is usually an uncommon rather than guaranteed sighting.
There's no strong season in the data, so it can be seen year-round. Its comfort range of roughly 23 to 29C matches typical water temperatures in Costa Rica and the Galápagos throughout the year.
Look for a small, deep-bodied damselfish around 13 cm, coloured dusky grey-brown with faint vertical bars rather than bold stripes. It sticks close to rocky reef structure and grazes algae rather than swimming in open water.
They typically reach around 13 cm in length, making them one of the smaller, easier-to-overlook damselfish on Eastern Pacific reefs.
No, they pose no threat to divers. They may become mildly territorial if you linger near a nest site, but there's no real risk involved in approaching them.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
Yellowtail Clownfish
3,523 sites
