Yellowtail Damselfish in Cozumel

Adults are dark brown-blue with a bright yellow tail. Juveniles — often called jewelfish — are deep blue scattered with brilliant electric blue spots.

Quick ID

Where You Will See It In Cozumel

Yellowtail Damselfish works the 3 to 49 foot band. On this island that means the sheltered west-coast reefs, and the shallow east-side entries when the sea is flat — these are the sites where the depth and the habitat line up for it.

Without a boat. It is worth looking for at El Mirador, El Presidente and Money Bar — all shore entries, so you dive them on your own schedule.

On an ordinary beginner boat dive. It should be within reach at Paradise, Punta Dalila, San Clemente, Yellow House and Casa Blanca. No advanced certification needed.

Deeper, and on the walls. It is also plausible on San Juan, Barracuda Reef, C-53 Wreck and Los Atolones.

Conditions change the odds more than the site does — the current, the time of day and how much the group has already stirred up the sand. Ask your guide what they have been seeing that week.

Behaviour

Fiercely territorial farmers. They cultivate patches of algae, weed out the species they do not want, and charge fish many times their size — including divers who hover too long over the patch.

Commonly Confused With

• Other damselfish — The bright yellow tail on a dark body identifies the adult; the electric blue spots identify the juvenile.
• Blue chromis — Blue chromis are slender, bright blue and school in open water.

Diving Etiquette And Safety

Nothing required beyond amusement. A damselfish charging your mask is defending a patch of algae, not attacking.

Part of the Cozumel marine life guide · see Cozumel dive sites · plan your Cozumel dive trip

Photo: Paul Asman and Jill Lenoble, CC BY 2.0, via Wikimedia Commons.