From the Super Mario Wiki
Bubbas are big pink or orange fish (usually wearing sunglasses) that will eat Mario if he gets too near them after a while. They look and act very similar to Boss Bass from Super Mario Bros. 3. Bubba appears to be a species of Blurp. Related to them is the small Bub fish.
Super Mario 64
Two Bubbas appear in Tiny-Huge Island and they cannot be defeated similar to most aquatic enemies in Super Mario 64. If Mario is eaten, he will lose a life, regardless of his current health. In Super Mario 64 DS, they are replaced by Big Berthas.
Additionally, stepping on a Happening Space on Yoshi's Tropical Island, a gameboard in Mario Party, Bubba would eat Toad, switching Toad's and Bowser's position. Bubba lacks its trademark shades in this game, which makes it look more like Bub.