The rock greenling varies its color to better match its surroundings. Males may have red blotches on their sides so the one pictured above is a male. They have a single dorsal fin that is divided in a front section and a back section with each section divided by a notch giving it the appearance of having two dorsal fins.
Rock greenling range from the middle of California northward to alaska and continuing around to the bering sea and again sout to Japan. They grow to a maximum size of about two feet long.
The have a somewhat surprising diet. Rock greenling feed mostly on fish eggs and larvae and planktonic crustaceans. Quite small food for a fish with such a large mouth.
They prefer rocky shallow water habitats.