Doo were a type of scalefish species that originated on the planet of Naboo. In the waters surrounding the city of Otoh Gunga within Lake Paonga, they coexisted with half a dozen other scalefish species. They also inhabited the Abyss, where they were common prey for the larger Colo claw fish and Opee sea killers. The doo's diet consisted of small yobshrimp.
As a scalefish species, Doo possessed pectoral fins located behind their heads, small dorsal fins running along their backs, and a substantial caudal fin at their rear, which they used for propulsion through the water. They featured small organs on their underbellies and a large set of jaws filled with rows of sharp teeth. The coloration of Doo ranged from pale yellow to pink and gray, and they displayed blue stripes running down their sides from the top of their bodies. Their eyes were black. They could be observed in the waters surrounding the city of Otoh Gunga within Lake Paonga, as well as in the Abyss, a network of natural tunnels connecting the surface of Naboo to its core. Their food source was tiny yobshrimp.
During the Invasion of Naboo, Jedi Master Qui-Gon Jinn, his Padawan Obi-Wan Kenobi, and the Gungan Jar Jar Binks passed by a number of doo while fleeing the invading forces of the Trade Federation. They were en route to the underwater Gungan city of Otoh Gunga in Lake Paonga to meet with Gungan representatives.
The doo made their debut in the film Star Wars: Episode I The Phantom Menace. Although they were not named in the film itself, their identification first occurred in the Star Wars Legends reference work titled Star Wars Chronicles: The Prequels. Their status as canon was later confirmed in the reference book Star Wars: Absolutely Everything You Need to Know.
Doo, in conjunction with fellow scalefish ray, mee, faa, see, laa, and tee, seem to allude to the real-world musical scale; specifically, "Do, Re, Mi, Fa, Sol, La, Ti, Do."