A reef runs two shifts, and cardinalfish are the night crew.
At dusk the changeover happens in a few minutes and it is worth staying in the water to watch. The damselfish, wrasse and butterflyfish that spent the day in open water drop into the coral and wedge themselves into exactly the holes the cardinalfish have been sitting in all afternoon. The cardinalfish come out as they go in. The same square meter of reef is occupied around the clock by two different sets of animals that barely ever meet, using the same shelter in alternation.
So a snorkeler who only swims in daylight sees a handful of cardinalfish hanging quietly under a ledge and concludes they are a minor part of the fauna. Get in at dusk and the water above the coral fills with them.
This one is among the prettiest: translucent with bright yellow stripes down a silvery body and a dark bar through a very large eye. It hangs in small groups by day, spreads out over the reef at night for zooplankton, and, like the rest of the family, the male carries the eggs in his mouth.
The genus. Ostorhinchus Lacepède 1802 - osteo- (bone) + rhynchus (snout). ETYFish
The species. Ostorhinchus cyanosoma (Bleeker 1853) - cyano- (dark blue) + sṓma (body). ETYFish
- translucent silvery body with four to six bright yellow stripes
- large eye, dark bar through it
- hangs in small stationary groups under ledges and in coral by day
- up to 8 cm
