Sergeant fish, also known as damselfish, are small but aggressive fish found in tropical and subtropical waters. They get their name from their distinctive black and white stripes, which resemble the uniforms of military sergeants. However, there are several other synonyms for sergeant fish, including blue devil fish, convict fish, and sergeant majors. These fish are popular among aquarium enthusiasts for their vivid coloring and lively personalities. They can be found in a variety of aquatic habitats, from shallow reefs to deep ocean waters. While they may be small in size, sergeant fish are big on attitude and are known for their territorial behavior.