Damsel Fish
Scientific name Pomacentridae
Damselfish are small, colourful and incredibly common reef fish found throughout tropical oceans. Despite their size, they are famously bold and highly territorial.
Around Koh Tao, you’ll see damselfish in almost every shallow reef zone from 2–20 metres. Many species are electric blue, yellow or striped, while others — like the well-known Sergeant Major — display bold black-and-white bands.
They often hover just above coral heads or rocky patches, darting quickly back to shelter when approached. Some species actively farm patches of algae, fiercely defending their “gardens” from other fish — and sometimes even divers!
During breeding season, males guard eggs attached to hard surfaces and may charge at intruders to protect their nest.
Find Damsel Fish at...
Divemaster's tip
If a small fish repeatedly darts toward your mask or fins, you’ve likely entered its territory. Simply move a metre or two away and it will settle down.
Look closely at flat rock surfaces — you may spot a male guarding a patch of tiny eggs.
What do they eat?
Damselfish feed on algae, plankton and small invertebrates, depending on species.
By grazing algae and farming territories, they play an important role in shaping reef ecology and maintaining balance within coral communities.
