The Other Blue Chromis
What about the other Blue Chromis? Pretty much everyone who has been into a Local Fish Store has seen the Blue Green Reef Chromis, but what if I told you there was another one? Just as small, just as reef safe, just as stunning, and schooled just the same? A darker, starker cousin to the fish we all know is available, and if your goal is some thing a little different in the Chromis department, or maybe just one that is appropriate to your Caribbean reef, I have a great surprise for you. Chromis cyanea is the fish you've been looking for. As an aside, Chromis cyanea translates pretty much as “blue fish” which checks out with its pretty unimaginative common name: Blue Reef Chromis. They are also sometimes called Blue Damsel, and Sapphire Devil, though this one I believe to be a case of mistaken identity.
In the wild our diminutive friend can be found throughout the Tropical / Subtropical Caribbean and Western Atlantic, from South Carolina shore all the way to Brazil and pretty much everywhere in between as long as there is a reef or drop-off for them to school around. They live in groups around these habitats where they live on zooplankton, primarily copepods and other suspended foods. These schools will be interspersed with Creole Wrasses and Juvenile Black Snappers (Apsilus dentatus) which mimic the Blue Chromis. The record size for C. cyanea is 15 cm or almost 6 inches, a size that is pretty much unheard of in the wild or captivity.
Captive care of the Blue Reef Chromis is nearly identical to the care for the more commonly known Chromis species. They'll eat just about any food you throw at them; a rounded diet will ensure their immune systems stay strong and their colors stay vibrant. We feed them a mix of marine based meaty foods and high quality pellets. While the Blue Reef Chromis is a peaceful fish, it has a penchant for maintaining social structure through aggression. This means that groups should be given a lot of structure to escape from each other, and the numbers kept should be large. We recommend keeping no less than 7 and more would definitely be better if possible for you. When keeping larger groups, more daily feedings (obviously with less food per feeding) will help ensure everyone gets some food.
Substrate is not a requirement for keeping C. cyanea, but if you'd like to see them make and guard nests, a fine to medium grain sand bed will encourage this behavior. Males will make small areas of interrupted lines where the females will also likely lay eggs. Males will guard and aerate the eggs as well, as captive breeding is possible. However, once they hatch, the larval chromis will be fish food; rearing the fry is beyond the means of the vast majority of home aquarists. Professional aquarists at the New England aquarium have succeeded in rearing them through larval stage; a truly momentus accomplishment! You can read about this at Reef to Rainforest, the link is included below! We are still a long way away from having commercially available levels of production though.
All in all, the Blue Reef Chromis is a great fish for the home aquarium, they are hardy and small, offer brilliant blue coloration and high activity without major concerns about aggression with your other fish. While they are not as readily available as some of the other Chromis genus fish, they shouldn't be overlooked when planning out your display. Ask your LFS about sustainably harvested Blue Reef Chromis from Quality Marine.
https://www.fishbase.se/summary/chromis-cyanea.html
https://biogeodb.stri.si.edu/caribbean/en/thefishes/species/3869
https://www.reef2rainforest.com/2016/12/31/breeding-the-blue-reef-chromis/