Pomacanthus arcuatus is one of the 13 members of the genus Pomacanthus, which together with 7 additional genera make up the family of angelfishes (Pomacanthidae) in which a total of 89 species are currently described. It is a relatively common species found in the reefs and rocky areas of the western Atlantic Ocean, from New York to Rio de Janeiro.
The body of Pomacanthus arcuatus is short, relatively tall and laterally compressed, with a nearly circular shape. It has a short snout with a small terminal mouth. They possess a spine at the angle of the preoperculum. The dorsal fin has 9 spines and 31-33 soft rays, and the anal fin has 3 spines and 23-25 soft rays. The anterior portions of the soft ray of both the dorsal and anal fins extend into thin filaments in adult specimens, the outline of both fins behind these filaments being convex in shape. The pectoral fins have 19-20 rays, the pelvic fins extend behind the first spines of the anal fin, and the caudal fin is emarginate in adults and rounded in juveniles.
In adult specimens of Pomacanthus arcuatus, the body is covered with dark-colored scales, with pale edges, giving the body a grayish color. The dorsal, anal and caudal fins are gray with darker colored margins, and finally a thin white line. Also noteworthy is the region of the mouth and its surroundings that tend to be a lighter gray or even white in some specimens. The juveniles of this species have the coloration of the head, body and fins black, and add to their livery 5 vertical stripes, light yellow: the first behind the mouth, the second behind the eye, the third from the center of the dorsal fin to the belly, the fourth from the posterior third of the dorsal fin to the center of the anal fin, and the fifth stripe at the base of the caudal fin, which is bordered with yellow. The back of the pelvic fins and the tip of the anal fin are blue.
The diet of Pomacanthus arcuatus is based mainly on sponges, tunicates, bryozoans and some coral polyps such as Zoantharia and Gorgonia, as well as sporadically certain algae and some crustaceans such as amphipods and copepods.
Adult specimens of Pomacanthus arcuatus are easily distinguishable from Pomacanthus paru. Pomacanthus arcuatus is grayish-brown with whitish scale edges, while Pomacanthus paru is dark brown to black with bright yellow scale edges. Additionally, Pomacanthus arcuatus has 9 spines on the dorsal fin and an emarginate caudal fin, while Pomacanthus paru has 10 spines and a rounded caudal fin. It is much more difficult to differentiate between juveniles of both species, in which case it is necessary to check the middle stripe present on the rostrum and the color of the posterior edge of the caudal fin.Photos: