Sergeant Major fish
The Sergeant Major fish is a small, rounded fish with the body compressed laterally. It has a single nostril on each side of the snout, rather than two as in the butterflyfishes and angelfishes. The mouth is small and terminal. This fish is often confused with Abudefduf taurus, the night sergeant. However, the vertical bars of the sergeant major are more pronounced and it has a slimmer body. There is also much less distance between the eye and the upper margin of the mouth in A. saxatilis than in A. taurus.
There are two color phases: the light phase is observed when the fish is over a light sandy bottom or swimming above the reef while the dark phase is evident when the fish is hiding among the rocks and crevices within the reef. The light phase is characterized by the gray coloration of the lower body and entire head, often with a hint of green. The upper third of the body is yellow while the soft dorsal, caudal, and anal fins appear dusky. There are five prominent vertical black bars on the body, becoming narrow toward the belly. Sometimes a faint sixth bar may be seen on the caudal penduncle. There is a black spot at the upper base of the pectoral fin. In dark phase fish, the body is dark gray or bluish with the color sometimes dark enough to hide the black vertical body bands. This coloration is also often observed in the males during spawning and nest guarding activities. Juveniles are always in the light coloration phase except for those associated with sargassum communities. Occasionally the juveniles appear solid black but never at sizes larger than 20mm. The vertical black bars may be indistinct on very young individuals and the fins colorless.