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 (like Deb (& Flo) for example). Bloat is from "Bob's Fish Mart".
In the ending of the film, Bloat and the rest of the Tank Gang escape the aquarium exactly as Gill had planned, but Bloat then asks, "Now what?!" ending the gang's joy of escape and causing them to worry about how they will get out of their plastic bags. However, during the credits, the tank fish have escaped their bags somehow. As the credits continue to roll, Bloat is seen having a brief dispute with Gurgle. He then bloats up, and Gill and Gurgle start spiking Bloat around like a volleyball.