Cocoa DamselfishStegastes veriabilis
The Cocoa Damselfish is difficult to distinguish from the Beaugregory. Most often the Cocoa Damselfish can be identified by the presence of a dark spot of 'cocoa' at the base of the dorsal fin. (but sometimes the Beaugregory juveniles also present the same spot.) Another way to help identify the Cocoa is to look at the way the rows of it's side scales line up. They seem to form straight vertical lines on the sides of their bodies. The juvenile's circular dorsal fin spot is positioned so that half the circle is ON the body, not entirely located on the dorsal fin as is the Beaugregory's.
Another clue is the Cocoa Damsel's habitat which differs from the Beaugregory. The Cocoa like the fore reef areas whereas the Beaugregory prefers the back reef areas. Even with all that information, it's still hard to tell when the fish is in an intermediate stage and the dorsal fin spot is fading.