Sergeant Majors of the Atlantic Ocean

A common visitor for snorkelers and divers is the sergeant major fish! This species is a coral reef fish that is found in many reefs in the Atlantic Ocean.  They are common in tropical and subtropical shallows all over the world.  This fish adopted its name sergeant major because of the five black bars that resemble the insignia of that rank in the military services.  The Sergeant Major fish scientific name is Abudefduf saxatilisWhich stands for Abudefduf  (father) saxa (living among rocks) tilus (tile-like in color).  It’s called “father” is because it is aggressive and bossy to the other inhabitants of a reef. And many divers can attest! If you invade their territory and you’ll often receive a chasing nip at your fins as you pass by their clutches of eggs.


During the months of April – August mating occurs and territories are established for reproduction.  This is when  the male is extremely territorial. The male will select a nest site and prepare it for mating.  He will then begin courtship and encourage females to deposit their eggs at his nest.  Also, during mating the male of the species becomes deep blue (see photo below) and guards their eggs. The male is left to guard these clutches of eggs, many times containing eggs from multiple females.  You can most easily determine male and female during mating season, as the males become a bright blue and guard their nests.  Many damsel fish change sex over their lifetimes, beginning as male, and then as they grow, become female.


The adults will often form large feeding aggregations that patrol the area. You can many times see them together underneath boats as we tie off to the reefs for snorkeling and diving. They feed upon the larvae of invertebrates, zooplankton, smaller fish, crustaceans, and various species of algae.


Sergeant Major Fish