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Atlantic Sergeant Major

abudefduf saxatilis

The Atlantic Sergeant Major (Abudefduf saxatilis) is a vibrant and boisterous damselfish known for its energetic presence across shallow Atlantic coral reefs. Taking its common name from the distinct vertical black stripes that resemble the insignia of a military rank, this highly visible species is a staple of tropical marine environments. Often seen darting through the water column in large, dynamic schools, they are constantly on the move, foraging for plankton and algae. During the breeding season, the typically yellow and white males undergo a striking transformation, adopting a dark blue hue as they fiercely guard their nests against any intruders. Their adaptability to various habitats, including coral reefs, rocky shores, and artificial structures, makes them one of the most frequently encountered and entertaining fishes for snorkelers and marine enthusiasts exploring the Atlantic coastlines.

Habitat: Typically found in shallow, warm marine waters, this species thrives in coral reefs, rocky coastal zones, and around artificial structures like shipwrecks and piers.

Appearance

The Atlantic Sergeant Major is characterized by a laterally compressed, oval-shaped body that typically reaches lengths of 15 to 20 centimeters. Its most identifying feature is the pattern of five prominent vertical black bars running down its sides. The upper portion of the body and back are usually a bright, eye-catching yellow, which fades into a silvery-white or pale gray on the lower half and belly. During the reproductive phase, nesting males exhibit a dramatic color shift, turning a dark, purplish-blue to signal their territory and breeding status.

KingdomAnimaliaPhylumChordataClassActinopterygiiOrderBlenniiformesFamilyPomacentridaeGenusAbudefduf

Atlantic Sergeant Major

Interesting facts

Males prepare the nest by vigorously cleaning a patch of bare rock, and once the female lays the eggs, he takes over all parenting duties.

The eggs of a Sergeant Major are brightly colored, transitioning from an intense red to a greenish hue as they develop and get closer to hatching.

Their name 'Sergeant Major' comes from their five black stripes, which closely resemble the military insignia of that rank.

They are known to form massive feeding aggregations of up to several hundred individuals, creating a moving wall of stripes over the reef.

Special abilities

Nesting males can rapidly change their typical yellow coloration to a deep, dark blue to signal their reproductive state and claim territory.

When guarding their purple-colored egg patches, males become hyper-aggressive, fearlessly chasing away much larger fish and even human divers.

During their larval stage, they often seek shelter in floating rafts of Sargassum seaweed, allowing ocean currents to disperse them across vast distances.

Measurements & details

Length: 15-23 cm
Weight: 0.05-0.2 kg
Lifespan: 3-5 years
Clutch Size: 10000-25000
Incubation: 3-5 days

Diet & Feeding

They are opportunistic feeders that forage both in the water column and on the substrate, consuming a wide mix of plant and animal matter.

Age differences: Juveniles tend to feed more heavily on algae and small invertebrates found in tide pools or Sargassum, while adults actively hunt larger zooplankton in the water column.

Primary Foods

Zooplankton
Benthic algae
Small crustaceans
Invertebrate larvae

Foraging Method

Foraging

Ecological connections

eaten by

Nassau Grouper

Epinephelus striatus

Serves as a primary food source for larger predatory reef fish.

mutualism

Green Sea Turtle

Chelonia mydas

Sergeant majors occasionally clean parasites and dead skin off marine turtles.

competitor

Bicolor Damselfish

Stegastes partitus

Competes with other damselfish species for food and nesting territory.

Traits

No trait badges are assigned for this object yet.

Also known as

No aliases listed yet.

Collections

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Safety

Danger

1/5 · Very low

No special safety notes yet.

Frequently Asked Questions

How long is Atlantic Sergeant Major?

15-23 cm

How much does Atlantic Sergeant Major weigh?

0.05-0.2 kg

How long does Atlantic Sergeant Major live?

3-5 years

What does Atlantic Sergeant Major eat?

They are opportunistic feeders that forage both in the water column and on the substrate, consuming a wide mix of plant and animal matter.

Where is Atlantic Sergeant Major usually found?

Typically found in shallow, warm marine waters, this species thrives in coral reefs, rocky coastal zones, and around artificial structures like shipwrecks and piers.

How does Atlantic Sergeant Major hunt?

Foraging

How many eggs does Atlantic Sergeant Major lay?

10000-25000

How long do Atlantic Sergeant Major eggs take to hatch?

3-5 days