Bloat is a porcupine pufferfish who lives in Philip Sherman's office tank. When he gets scared or agitated, he bloats up, and then one of the other fish has to deflate him. He likes to be as disgusting as possible.
Bloat is first seen swimming and approaching Nemo hiding into a diving helmet decoration, along with Bubbles, Deb, 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, Bloat says he is from a fish emporium called "Bob's Fish. Mart". Suddenly, Bloat is seen arguing with Gurgle to know what tool the dentist is using on the patient in which he inflates after yelling at him while Deb deflates him. Later, Bloat, along with Gurgle, Bubbles, and Deb, 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, Bloat 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, Bloat, along with Gurgle and Deb, 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, Bloat 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, Bloat starts to play in the dirty tank while Gurgle tells him not to play with the algae in the tank. The next day, Bloat 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. Suddenly after Gurgle is enraged that the AquaScum 2003 is installed into the tank, Bloat is worried that the escape plan Gill taught them is ruined. Bloat is later seen along with Gurgle, Deb, Bubbles, and Jacques helping Gill stop Darla from harming Nemo. Bloat and the rest of the Tank Gang are seen congratulating Gill for saving Nemo from Darla.
During the epilogue, Bloat and the rest of the Tank Gang escape the aquarium exactly as Gill had planned and later seen cheering on Peach who successfully makes her way to the ocean However, Bloat then asks the rest of the Tank Gang, "Now what?", ending the gang's joy of escape and causing them to worry about how they will get out of their plastic bags. During the credits, Bloat is seen having a brief dispute with Gurgle. He then inflates, and Gill and Gurgle start spiking Bloat around and using him like a volleyball. Jacques is later seen running and jumping on Bloat who has inflated.
Bloat and the rest of the Tank Gang are seen at the post credits of the film, still trapped in their algae-covered plastic bags. He and the rest of the Tank Gang are captured by two Marine Life Institute volunteers upon arriving in Morro Bay.
Like all pufferfish, Bloat sucks water into a compartment in his stomach to inflate, and also like many pufferfish in real life, Bloat often has trouble deflating.
Bloat doesn't have chameleon-like eyes and color-changing abilities that real pufferfish do.
Bloat with Nemo
Gill's escape plan finally succeeds...except they're still stuck in plastic baggies, with no idea how to get out of them.