by B. N. Sullivan
This photo is dominated by a grouping of Pyramid Butterflyfish (Hemitaurichthys polylepis). Their common name refers to the triangle-shaped white patch that covers most of their bodies. These plankton eaters tend to aggregate over stands of coral during daylight hours, just as you see in the photo. Pyramids are native to the central and western Pacific Ocean.
In the lower left quadrant of the photo are some Milletseed Butterflyfish (Chaetodon miliaris), named for the vertical rows of black seed-like dots on their otherwise yellow bodies. They also sport a prominent black ocular bar (eye-stripe) and a black blotch at the base of their tails (i.e., the caudal peduncle). They, too, eat plankton, but sometimes a diver or snorkeler will see a Milletseed Butterflyfish cleaning other fishes.
The Milletseed Butterflyfish is a Hawaiian endemic species -- that is, they are found naturally only in the Hawaiian Islands. They are quite plentiful along coastal reefs, so if you snorkel or dive in Hawaii, you are very likely to see these fishes.
The photo on this page was taken at Big Sandy, a dive site located a few miles north of Kawaihae, on the North Kohala Coast of the Big Island.