Apogon erythrinus

The Hawaiian ruby cardinalfish is a relatively small red fish with a somewhat transparent appearance. The Hawaiian Ruby Cardinalfish has a second dorsal fin spine that reaches at least to the base of the third ray of its second dorsal fin when depressed. It also has 14 pectoral fin rays.[3]

They can grow up to 1.57" (4 cm).[4]

The Hawaiian ruby cardinalfish is located in the Eastern Central Pacific waters, known only from the Hawaiian islands and Johnston Island. There have been reports of occurrence in other Indo-West Pacific countries though it is questionable.

These fish reside near shore upto depths of 300m. They are mostly found in coral or rocky reefs, although some still inhabit seagrass, coralline algal meadows, soft-bottom communities, estuaries, and lowland freshwater of warm temperature waters.[5]

Hawaiian ruby cardinalfish can be found while snorkeling near shallow shores, as these fish tend to not stray far from its shelter,[1] however, they are observed to be active only at night.[1] They are mostly observed through the months of July through October.