Pacific Double-saddle Butterflyfish

Appearance

These fish can reach a size of 15 cm. They are white with vertical thin black lines down the body and two dark saddles on the fore and hind back, which softly grade into the background color bellywards gradient. Immediately after the hind quarter saddle, the body and tail is bright yellow with a black spot on the caudal peduncle. The dorsal fin has a streak of yellow from the crown of the head to the tail. Like most of its relatives this species displays a black eye band like a mask. As in most butterflyfish, the Pacific double-saddle butterflyfish is prone to blanching at night and when startled.

It belongs to the large subgenus ''Rabdophorus'' which might warrant recognition as a distinct genus. In this group, the closest relative of this peculiar species is the similar-looking Black-wedged Butterflyfish, ''C. falcula''. Other fairly close relatives are the quite differently-shaped but similarly-colored Lined and Spot-naped butterflyfishes, while the Blue-cheeked Butterflyfish seems to be a far more basal lineage relative to all of these. The vertical lines are present in all of these, while a white body with yellow behind and black on back and caudal peduncle are only shared among the four less ancient species.

Habitat

''C. ulietensis'' is often found singly or in pairs on coral-rich reef systems, foraging on sessile invertebrates and algae. It is not a territorial species that freely grazes throughout a wide range within reefs, lagoons and harbors, and every now and then large groups congregate at rich feeding spots. It is rarely ever observed in a deep reef environment or the open sea; juveniles are typically reared in shallow lagoons, estuaries or harbors.

An opportunistic omnivore, diet consists mainly of microscopic algae, other plankton, and small sessile invertebrates. As a measure of defense, they typically wedge themselves in tight crevasses to escape predators.