This section is from the book "American Game Fishes", by W. A. Perry. Also available from Amazon: American Game Fishes: Their Habits, Habitat, and Peculiarities; How, When, and Where to Angle for Them.
Body deep and rather short, the profile high and strongly curved; dorsal outline convex; depth more than half the length; head with flap a little less; dorsal spines low, lower than in most of the other species, in adults shorter than from snout to middle of eye; pectorals not reaching vent; gill-rakers very short and soft; opercular flap very long in adult, always with broad pale edge which is pinkish behind and bluish in front; in young specimens the flap exhibits every stage of development, no two individuals being alike in this respect. Colors very brilliant, more so than in any other of our Sun-fishes, but fading rapidly after death. The general color of an adult specimen is brilliant blue and orange, the black chiefly blue, the belly entirely orange, the orange forming irregular longitudinal rows of spots, the blue in wavy vertical lines along the series of scales; vertical fins with the soft rays blue and the membranes orange, sometimes fiery red; ventral and anal, dusky blue; lips blue; cheeks with blue and orange stripes; top of head and neck black; iris bright red; fins unspotted; young specimens with the ear-flap small, and the coloration variously dull; D. X, 10; A. Ill, 10; lat. I. 40.
Throughout the Mississippi valley, and on south-westward to the Rio Grande, this gorgeous little fish is abundant. It is also occasionally taken in the streams of the North-west, it may be found on every urchin's string in Indiana and Illinois. It is smaller than the common Sun-fish, and less active, although in coloration it is one of the gayest fishes that swim.