Mouse is a field mouse that appears in the episode credits. She is voiced by Vanessa Marshall.
She enjoys watching the fish in the tanks, and is a little more short-tempered than her friend, Snake. Mouse and Snake always appear in the end credits, usually talking about what the episode is about such as pets, adulthood, football, and humor.
- Mouse wants to have a late night talk show ("Hooray for Hamsterwood", "The Tale of Sir Oscar Fish").
- Mouse and Snake used to have a band.
She has appeared in all of the credits (except for "Fish School Musical") so far, had a cameo at the beginning of "Hooray for Hamsterwood" when she jumped over Bud with a motorcycle, made a cameo at the cheer-off in We've Got Fish Spirit, and a cameo with Snake in Halloween Haul.