Appearance
Sergeant majors have a flattened body that can be up to 9 inches (23 cm) long. Inside their tiny mouths are pointy little teeth. This fish is called a sergeant major because of its five vertical black bars on its sides. The last bar is found on the caudal peduncleor area connecting the tail to the body. During mating season, the adult males change almost completely to dark blue, making it hard to see the black bars. Sergeant majors have a large eye and a very small mouth.

Depending on its surroundings, the sergeant major slightly changes its coloration to camouflage itself. Over sand flats, this fish’s main coloring becomes muted. Over dark areas, this fish changes almost entirely to black, making the bars invisible.

Habitat
Sergeant majors live in large groups up to several hundred individuals on and around coral reefs, tidepools, seagrass beds and sand flats to depths of 50 feet (15 m). Juveniles are most common in tidepools.

Range
Sergeant majors live in the warm waters of all the oceans around the whole world.

Diet
Sergeant majors graze on small crabs, shrimp, and fish, invertebrate babies, and algae. Often swimming out in the open, they also eat phytoplankton or tiny plants and zooplankton or tiny animals. Sergeant majors aren’t picky eaters. They eat such a wide variety of foods depending on what’s available where they live. If algae is overriding the reef, the sergeant major’s diet will almost completely consist of this green cuisine.

Adults frequently form large feeding schools up to several hundred individuals. A large group of fish confuses predators, making it almost impossible for the predator to focus on one sergeant major. Also, a big school of fish may look like a large fish from far away, which also makes most predators steer clear.

Reproduction
A certain phase in the moon cycle and the warming of the ocean in the months from April to August trigger mating in the sergeant majors. In order to attract females, male sergeant majors change their color, darkening their hues. This is an important part of their mating ritual, since the males and the females look exactly the same at the other times of the year.

These fish will mate more than once in one mating season. The females will deposit up to 200,000 eggs at a time. They lay the oval shaped eggs in a sheltered area on a bed of algae, or near a coral head. In the morning, the male fertilizes the eggs. Remaining this blue color, the males are territorial, which means they ferociously guard the territory where the eggs are laid. After about four days, the eggs hatch and the male returns to its normal colors. The newly hatched larvae swim on up to the epipelagic zone or the zone in the open ocean near the surface. The larvae float here until they reach a certain size. After they are large enough, these young sergeant majors drop down and join the other reef creatures. The young often end up at a different reef from their parents. This keeps this species from only being found on one reef in one specific area.

A species or group of organisms that is in danger of extinction or disappearing from the face of the earth in the near future if its situation is not improved.

A species that can be found throughout its natural range but is declining in number and may become endangered in the absence of special protection efforts.

A species that is not declining in number but is of special concern because it is sensitive to pressure by particular human activities or natural events.

A species that is not declining in number and is not sensitive to pressures by human activities or natural events.

Threats and Management
Destruction of coral reefs and the other habitats of the sergeant major threaten the stability of their population. These fish are also popular in the pet trade. They are easily found in pet stores.

Did You Know?
Damselfish are easy to keep in the home aquarium, but they are also one of the most menacing fish, often picking on other fish and stressing them out to the point of death.

The scientific name Abudefduf saxatilis means "A tile-like fish that lives among rocks and is the father of the reef" (Abudefduf – father, saxa – living among rocks, tilus – tile-like in color). It is believed they are called “the father of the reef" because of their aggressive nature, being able to “tell" other fish what to do.

References
Web Sites
NOTE: The following Web sites are not maintained by the John G. Shedd Aquarium and will open in a new browser window.

Fishbase:
http://filaman.uni-kiel.de/Summary/SpeciesSummary.cfm? ID=1119&genusname=Abudefduf&speciesname=saxatilis

Print Publications

Debelius, H. 1999. Indian Ocean Reef Guide. Frankfurt, Germany: IKAN. 321p.
ISBN# 3-9317-0267-7.

Lowe-McConnell, R.H. 1987. Ecological Studies in Tropical Fish Communities. New York, New York. Cambridge University Press. 382 p. ISBN# 0-5212-8064-8.

Michael, S.W. 1998. Reef Fishes. Shelburne, Vermont: Microcosm. 624p.
ISBN# 1-890087-21-1.

Myers, R.F. 1999. Micronesian Reef Fishes. Barrigada, Guam: Coral Graphics. 216p.
ISBN# 0-9621564-4-2.

Perrine, D. 1997. Mysteries of the Sea. Lincolnwood, Illinois: Publications International, Ltd. 312p. ISBN# 0-7853-2430-5.

Wilson, R. and Wilson, J.Q. 1985. Watching Fishes. New York, New York: Harper Collins Publishers. 275 p. ISBN# 0-0601-5371-7.

Vocabulary Words

Caudal – Having to do with the end or tail of an animal. The tail fin.


Caudal peduncle – The narrow part of the body between the body of the fish and the caudal fin.


Dorsal – The back of an animal. The large fin on the back of a fish.


Epipelagic zone – The zone of the open ocean near the surface.


Extinction – An organism that has not been present on the face of the earth for over 50 years.


Invertebrate – An animal without a backbone.


Organism – A living thing.


Pectoral – The paired fins on the sides of a fish behind the gills.


Pet trade – An industry or business in which animals are taken from the wild and sold to pet stores, zoos, and aquariums.


Phytoplankton – Microscopic plants that float at the mercy of the ocean currents


Sand flat – A flat sandy area without plants or algae.


Seagrass bed – A coastal ecosystem mainly inhabited by marine plants like seagrass as well as some fish, urchins, sea stars and corals.


Species – A group of organisms capable of breeding and producing fertile offspring; organisms that share the same gene pool.


Territorial – An animal that lives in the same area all the time. This animal reproduces this area and fiercely defends it.


Tidepool – The water left in a depression or pool when the tide goes out. The shoreline area that experiences times of flooding and dryness due to a change in the tide. Animals common to tidepools are urchins, sea stars and small fish. There is also an abundance of seaweed, seagrass and algae.


Ventral – The belly of an animal.


Zooplankton – Microscopic animals that float at the mercy of the ocean currents and have weak swimming ability.