Square-spot goatfish are quite common and most easily distinguished by the square spot in the yellow stripe along their sides. However, the intensity of the square spot changes, darker during feeding, and fading (as with the fish in the photo) or disappearing altogether while resting or schooling. When the spot disappears, square-spot goatfish are hard to distinguish from yellowfin goatfish.

In my attempts to identify what I see in the water, I use John P. Hoover’s book The Ultimate Guide to Hawaiian Reef Fishes, Sea Turtles, Dolphins, Whales, and Seals. His website is hawaiisfishes.com.