Chromis viridis
Tiny electric-blue reef fish clouds hang over coral from Egypt's Marsa Alam to the Maldives' Central Atolls, year-round in 25-29 C water.
A tiny, deep-bodied fish rarely more than 7 cm, glowing pale blue to green with a faint silvery sheen depending on the light. It has a slightly forked tail and no bold stripes or spots, so the giveaway is really the colour plus the habit of massing in loose clouds just above branching coral. Up close the fins are translucent and the body is almost see-through at the edges, giving it a slightly ghostly look against darker coral heads.
Look for it hovering in loose, shifting clouds a metre or so above branching coral, picking plankton out of the water column in a constant nervous flicker. When a diver approaches, the whole group tends to dive into the coral branches together rather than scatter individually, then re-emerge once you back off. Most sightings are on shallow reef tops in daylight, often the first fish you notice on a reef crest before you spot anything bigger.
Whole groups sleep tucked inside the same branching coral head they feed over by day, using it as both a pantry and a bedroom.
No clear seasonal pattern shows up in the sightings, and with a comfortable range of about 24.6 to 29.3 C, it sits on shallow reef tops all year round. Plan around your destination's general dive season rather than a chromis-specific window.
Reef neighbours a diver could mistake it for. Use the identification notes above to tell them apart.
This is one of the most widely logged damselfish on tropical reefs, with the strongest numbers from Egypt's Red Sea, especially Marsa Alam and the Deep South and South Sinai, and from the Maldives' Central Atolls. It also turns up reliably in French Polynesia's Society Islands, on Australia's Queensland reefs, and around Indonesia, Mauritius's Flic-en-Flac, Japan's Okinawa and Ryukyu Islands, and Fiji.
Mapping where Blue-green Chromis is logged…
They are a near-constant presence on shallow reef tops, most heavily logged in Egypt's Red Sea (Marsa Alam, South Sinai) and the Maldives' Central Atolls, plus strong numbers in French Polynesia's Society Islands, Queensland, Indonesia, Mauritius and Japan's Ryukyu Islands.
There's no strong season in the data, they sit comfortably in 24.6 to 29.3 C water and are seen on shallow reefs throughout the year, so timing depends more on your destination's general diving season.
Look for a small, roughly 7 cm fish with a plain pale blue-green body and a lightly forked tail, hovering in loose clouds just above branching coral rather than sitting alone. There are no stripes, spots or bold markings, so the schooling behaviour over coral is as useful as the colour itself.
They top out at around 7 cm, making them one of the smaller fish you'll see clouding over a reef crest.
They mostly hover in single-species clouds above branching coral, and the whole group tends to dive into the same coral head together when a diver gets close, only to drift back out once things settle.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
Yellowtail Clownfish
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