(Chaetodontoplus septentrionalis )
1st time see one...

Also known as Coralfishes, Blue-striped Angelfish, Blueline Angelfish, Blue-lined Angelfish, Blueline Angel, Blue-banded Angelfish and Northern Angelfish.

Found singly in coral rich areas of rocky coastal reefs and lagoons.
They feed on sponges, algae and benthic invertebrates.
Length - 20cm
Depth - 5-60m
Widespread Western Pacific

Butterflyfish and Angelfish are members of the bristletooth family (Chaetodontidae) they have very fine hairlike teeth that enable them to pick out small organisms inaccessible to most other fish for eating.
Butterflyfishes thrive on a diet of coral polyps, tentacles of featherdusters and Christmas-tree worms. As these food sources all zap back into their shells the butterflyfishes need to be able to hover motionless while picking at the coral and to dart swiftly over short distances to get the worm before it retracts. They do this by using their Pectoral fins as oars to brake, sprint, turn and even reverse.