Flagtail also known as the Aholehole
The flagtails are a family (Kuhliidae) of perciform fish of the Indo-Pacific area. The family consists of several species in one genus, Kuhlia. Most are euryhaline and often found in brackish water, but the genus also includes species restricted to marine or fresh water.
The distinctive characteristic of these fish is a scaly sheath around the dorsal and anal fins. The dorsal fin is deeply notched between the 10 spines and the 9 to 13 soft rays. The opercle has two spines, and the anal fin three. Their bodies are compressed and silvery, and they tend to be small, growing to 50 cm at most.
During the day, they usually school, dispersing at night to feed on free-swimming fish and crustaceans.