Big Bertha

Big Berthas are huge Cheep Cheep that live deep in the sea. She has a counterpart called Boss Bass.

Super Mario Bros. 3
Big Berthas appear in the game Super Mario Bros. 3. In their debut, all Big Berthas seem to be mother fish, as they always carries Baby Cheeps in their mouth, occasionally letting them out. After a few seconds, the Baby Cheep will return to its mother's mouth. Unlike the active hunter Boss Bass (which is often seen aggressively swimming on or near the surface), Big Bertha is more gentle and nests comfortably underwater. If Mario or Luigi swims in her way, she may passively eat him (unless he's in frog form).

The Adventures of Super Mario Bros. 3
It is possible that Big Berthas made appearances on The Adventures of Super Mario Bros. 3. However, they were never seen with Baby Cheeps, usually chased after the good guys, and were never referred to by name. Whether these fish were supposed to be either Big Berthas or Boss Basses is unknown.

Nintendo Comics System
Bertha played a prominent role in the Nintendo Comics System. In her first appearance, Love Flounders, she falls in love with Frog Mario after being tricked by Stanley the Talking Fish. She eventually realizes Stanley was lying, but is consoled by Mario, who states he wants to be friends with Bertha, not lovers. Bertha later reappears in Fins and Roses, this time dating Stanley. She foils Wendy O. Koopa's plans by knocking the Koopa's bomb back at her.

Super Mario 64 DS
In Super Mario 64 DS, Big Berthas do not spit out Baby Cheeps, and replace Bubba from Super Mario 64. Like the Bubbas from the original game, they will aim in on Yoshi, Mario, Luigi, or Wario, mouth wide open, attempting to eat them. If a character is eaten, that character will lose a life, regardless of their current health. Also, the first Big Bertha can be defeated with a nearby Super Mushroom. In this game, it resembles a Cheep Chomp.

Trivia

 * A character named Big Bertha was featured in the Super Mario Bros. movie. Like the fish, she wore all red. Also, like the character in the comics, she had a crush on Mario.
 * In New Super Mario Bros. and its sequel, a similar enemy named Cheep Chomp appears, attempting to eat Mario and being a purple version of its appearance in Super Mario 64 DS.
 * The Cheep Cheep boss in Mario Party 9 resembles a Big Bertha.