If there is one fish almost every guest meets in Punta Cana, it is the sergeant major. Before you have even finished descending, a small crowd of yellow-and-black striped fish is often hanging in the water around you, watching to see if you have brought anything to eat. They are so common that many divers stop noticing them, which is a pity, because they have one of the most interesting family lives on the reef.

The sergeant major, Abudefduf saxatilis, is a damselfish, and during the breeding season the males turn dark blue and guard nests of eggs laid on rocks and wrecks, chasing off fish many times their size. Here is how to recognize it, what it is doing, and where to watch it.

Quick Facts

Name: sergeant major, Abudefduf saxatilis
Family: damselfishes (Pomacentridae)
Size: usually around 15 cm (6 in); the largest reach about 23 cm (9 in)
Diet: omnivore; algae, zooplankton, small crustaceans, invertebrate larvae and small fish
Depth: shallow water, from the surface to about 20 m (65 ft), most often above 10 to 15 m (33 to 50 ft)
Social life: loose schools that can grow to several hundred fish when feeding
Range: both sides of the Atlantic; in the west from Rhode Island through the Caribbean to Uruguay, in the east along West Africa
Status: listed as Least Concern by the IUCN

How to Recognize a Sergeant Major

The sergeant major is a small, oval, flattened fish with five bold black vertical bars on a whitish body, and sometimes a faint sixth bar at the base of the tail. The upper part of the body is washed with bright yellow. The stripes are said to recall the insignia on a military sergeant's sleeve, which is where the name comes from.

Breeding males look very different. While guarding a nest they turn dark gray or deep blue, and the black bars can almost disappear into the darker background. If you see a dark, bluish damselfish defending a patch of rock, there is a good chance it is a sergeant major on nest duty.

The look-alike to know is the night sergeant, Abudefduf taurus, a close relative that usually stays in very shallow, rocky water where the waves break. The sergeant major has bolder bars and a slimmer body. In the Indo-Pacific a similar species, the Indo-Pacific sergeant, takes its place, so the fish you meet in the Caribbean is always A. saxatilis.

Behavior: Plankton Pickers and Devoted Fathers

Most of the day, sergeant majors hang in the water column a little above the reef, picking zooplankton from the current and nibbling algae and small animals from the bottom. They are opportunists, and they learn quickly that people sometimes mean food. That is why they swarm around boats, snorkelers and divers, and why feeding them is such a bad habit: it changes their behavior and draws them away from their natural diet.

Breeding is where the species gets really interesting. A male picks a flat, clean surface, such as bare rock, a wreck, a piling or a reef outcrop, and courts females in the morning, leading them to his nest. The eggs stick to the surface and form a patch. Fresh eggs are deep red, then turn violet and greenish as the embryos develop, until they become almost clear and you can see the tiny silver eyes. A single nest often shows several colors at once because eggs of different ages sit side by side.

The male guards the nest for the whole incubation, which lasts about six to seven days. He fans the eggs with his fins to keep fresh water flowing over them and chases off anything that comes too close, including wrasses, much larger fish and curious divers. When the eggs hatch, the larvae drift off into open water. Young sergeant majors are often found in tide pools and under floating sargassum before they move onto the reef. The breeding season varies across the Caribbean, so we cannot promise you will see a nest on a given day.

Sergeant majors are also on the menu for larger hunters, including great barracuda and bar jacks. Our guides to the barracuda and the bar jack show the other side of that story.

Where to See Sergeant Majors in Punta Cana

Sergeant majors are common on almost every shallow dive and snorkel in the area, and they are usually one of the first fish our guests learn to name. They like structure close to the surface, so wrecks and artificial reefs are excellent places to find them. The Submarine, a tourist sub sunk in 1998 and now an artificial reef at 6 m (20 ft), is a good example, and the beginner reef at El Niño has plenty of them too.

To look for nests, check the flat, exposed surfaces of wrecks and rocks, and watch for a dark male holding his ground over a reddish or purplish patch. The engine and boiler of Wreck Monica at 15 m (50 ft) and the Atlantic Princess wreck on our Bayahibe day trip offer just the kind of surface they choose.

You will find the sergeant major on our species guide, next to other common reef fish such as the blue tang.

Tips for Divers and Snorkelers

Do not feed them. Bread, crackers or fish food may draw a crowd, but they are bad for the fish and the reef.
If a male rushes at you, you are too close to his nest. Back off slowly and watch from a little farther away.
Never touch an egg patch or the surface it sits on. The eggs are easily crushed or scraped away.
Snorkelers see sergeant majors easily, since they live close to the surface. Float calmly and let the school come to you.
For photos, try shooting a nest guard straight on at his level, with the egg patch in the frame.

Frequently Asked Questions

Why is it called a sergeant major?

Because of its bold black bars on a yellow and white body, which look like the stripes on a military sergeant's uniform.

Do sergeant major fish bite?

They have small mouths and are harmless, but a male guarding eggs may dash at a diver's mask or hand and give a tiny nip. It is a warning, not an attack.