Stegastes rectifraenum
A small, feisty reef fish found across Baja California, Mexico, active year-round in water from 19 to 26C.
Small, oval-bodied damselfish around 10cm, dark grey to brownish overall with a faint pale edge on the tail. Look for the compact, deep-chested shape typical of damselfish and its habit of holding a fixed patch of reef rather than roaming. Adults look fairly plain underwater, so it's the territorial behaviour over the colour that gives it away.
Expect to find it parked over a small patch of rock or reef that it defends against other fish, including divers who get too close to its turf. It's usually seen singly, holding station rather than schooling, and most sightings are logged as rare to uncommon at any given site, so it takes a bit of looking rather than being obvious on every dive.
Like other damselfish, it tends to cultivate a patch of algae on its home rock and will chase off intruders that stray onto it, a bit of housekeeping that's easy to spot if you watch one spot for a minute or two.
No strong seasonal pattern shows up in the sightings, and it sits comfortably in water from about 19 to 26C, so it's a reasonable year-round find on Baja reefs rather than a seasonal target.
Reef neighbours a diver could mistake it for. Use the identification notes above to tell them apart.
This one is a Baja California speciality, logged across dive sites the length of Mexico's Sea of Cortez and the Pacific side of the peninsula. It hasn't been reported outside Mexico in the data, so Baja is the place to look for it specifically.
Mapping where Cortez Damselfish is logged…
It's a Baja California specialty, turning up at dive sites right along the Sea of Cortez and Pacific coast of the peninsula in Mexico. Outside Baja it isn't part of the diver record, so this is the region to target.
There's no clear seasonal spike in sightings, and it tolerates a broad temperature range of roughly 19 to 26C, so divers report it fairly consistently across the year in Baja.
Look for a small, oval, dark grey-brown fish about 10cm long holding a fixed position on the reef rather than swimming freely. Its plain colouring and territorial, stay-put behaviour are the best clues, more than any bold pattern.
They max out around 10cm, making them one of the smaller reef residents you'll spot in Baja California.
No. They're too small to pose any risk, though they will dart at and nip fish, and occasionally divers, that get too close to their patch of reef.
At most sites where it's been logged, divers rate it rare to uncommon, with only a handful of sites reporting it as common. So it's around in Baja but not guaranteed on every dive.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
Yellowtail Clownfish
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