The sergeant majors are small, oval damselfish. It has a grey body with a yellow dorsal area. Most notably, they have five vertical blue-black bars across their bodies.
Although they sometimes form schools, the pair up during breeding. Breeding pairs have a preferred territory and will fight other fish to protect it. Once the eggs have been laid, the male will remain to guard and aerate them - this fierce behaviour is where they get their name "sergeant major" as well as their scientific name Abudefdul, with "abu" meaning father or guardian in Arabic.
They are omnivores and will opportunistically feed on algae and small invertebrates.
Juvenile sergeant majors are commonly found in tidal pools, while adults prefer rock and coral reefs on South Africa's Indian Ocean coasts. Globally, they occur throughout the Indo-Pacific, ranging from South Africa to the Red Sea, Japan and the Pitcairn Islands.