From Fish Hooks Wiki
Mouse is a House Mouse that is friends with Snake. She has a pink bow. They live together in a tank in Bud's Pets. Mouse mostly appears in the credits of episodes, but appears in "Hooray for Hamsterwood", "Halloween Haul", "So-fish-ticated", "Fish Prom" and the short "Merry Fishmas". Mouse is voiced by Vanessa Marshall.