Deb is a blue/black and white-striped humbug damselfish (or zebra damselfish) who lives in the dentist's fish tank in Sydney, Australia. She seems delusional, as she thinks her reflection is her sister named Flo, who may or may not exist.
Deb is first seen swimming and approaching Nemo hiding into a diving helmet decoration, along with Bubbles, Bloat, and Gurgle due to Nemo not feeling comfortable of living in the fish tank when he arrives. When Nemo asks the Tank Gang to know where his father is at and when Peach tells Nemo that his father Marlin may be at the pet store, Deb says that she is purchased by the dentist through a mail order. Deb is later seen talking to her reflection "Flo" after introducing herself to Nemo. Suddenly after Bloat and Gurgle argue to know which tool the dentist is using on a patient, Deb then deflates Bloat who has inflated after arguing with Gurgle. Later, Deb, along with Gurgle, Bubbles, and Bloat, try to get Nemo out of the tube whom he was trapped into, but a moorish idol named Gill stops them and tells Nemo if he could try escape the tube by himself in which Nemo successfully does so. Later that night, Deb and the rest of the Tank Gang accept Nemo into their group while Gill makes a plan to escape from the fish tank.
The next day, Deb, along with Bloat and Gurgle, is seen watching Nemo to do the escape plan and after Nemo successfully jams the filter fan with a pebble and the filter fan activates again, Deb and the rest of the Tank Gang rescue Nemo from falling into the filter fan. The next day when the Tank Gang makes the tank filthy, Deb is seen swimming around the tank looking for her reflection "Flo" while Gill tells Nemo and the rest of the Tank Gang that the dentist will clean the tank before Darla arrives to his office. The next day, Deb and the rest of the Tank Gang discover that the AquaScum 2003, an upgraded tank filter, was installed into the fish tank, preventing fish from escaping. Deb is later seen along with Bloat, Bubbles, Gurgle, and Jacques helping Gill stop Darla from harming Nemo. Deb and the rest of the Tank Gang are seen congratulating Gill for stopping Darla from harming Nemo.
During the epilogue, Deb and the rest of the Tank Gang manage to escape the fish tank. She and the rest of the Tank Gang (still in their plastic bags) are seen cheering on Peach who successfully makes her way to the ocean. During the credits, Deb is seen admiring her reflection in a bubble until a credit text pops it as there are no artificial glass walls surrounding her in the ocean.
Deb and the rest of the Tank Gang are seen at the post credits of the film, still trapped in their algae-covered plastic bags. She and the rest of the Tank Gang are captured by two Marine Life Institute volunteers upon arriving in Morro Bay.
Deb's name and her imaginary sister's together allude to "ebb and flow", the movement of water, often in relation to natural tides.
Eventually, Flo became the name of a character in the Cars series.
According to the credits and other media, Deb is listed as "Deb (and Flo)".
Deb could have actually had a sister named Flo back where she used to live.
Before Vicki Lewis voiced Deb the Damselfish, she played Dr. Else Chapman, the paleontologist in the 1998 sci-fi film Godzilla.
"Aww, He's scared to death."
Deb and her "sister" Flo
The Tank Gang finally succeed in escaping... only they are still in their plastic bags, with no idea of how to get out of them.