Sergeant Major

The Sergeant Major is a common and widespread damselfish (family Pomacentridae) named for the five dark vertical bars on its silvery body, resembling a sergeant's rank stripes. Native to the tropical and subtropical Atlantic, including the Caribbean and Gulf of Mexico, it is one of the most frequently encountered reef fish in its range. Closely related species with nearly identical patterns occur in the Indo-Pacific. Sergeant Majors are highly adaptable, tolerating a range of reef and nearshore habitats, and their populations are abundant and stable. They are a familiar sight to divers and snorkelers due to their bold markings and tendency to form large feeding aggregations.

• Body: Deep, oval, and moderately compressed
• Color: Silvery to pale yellow-green background
• Markings: Five distinct black vertical bars crossing the body, the clearest identifying feature
• Fins: Forked tail; dorsal fin often shows a yellowish tinge, especially in breeding males
• Size: Grows up to 23 cm, larger than most other Abudefduf species The five-bar pattern combined with its deep, silvery body distinguishes it from other similarly striped damselfish, though care should be taken with closely related Indo-Pacific look-alikes outside the Atlantic range.

Sergeant Majors are found throughout the tropical and subtropical western Atlantic, from the eastern United States and Bermuda south through the Caribbean to Brazil, with related populations in the eastern Atlantic and Indo-Pacific. They occupy a wide range of shallow habitats, from coral and rocky reefs to harbors, pilings, and seagrass edges, typically at depths of 1-15 meters. Water temperatures in their preferred range are generally 22-29°C. This adaptable species tolerates some turbidity and human-altered structure, often gathering in large numbers around docks, wrecks, and reef edges where currents concentrate plankton.

Sergeant Majors are highly social, forming large, loose schools that hover over reefs and structure to feed on drifting plankton, algae, and small invertebrates. During breeding season, males turn a deep blue-purple hue and become strongly territorial, clearing a patch of rock or dead coral to receive a female's eggs, which are laid in a sticky mass. The male then aggressively guards and fans the eggs, chasing off intruders many times his size, until they hatch after a few days. Outside of breeding, the species is relatively peaceful and gregarious, often mixing with other reef fish while foraging in open water above the reef.