Chuckles was one of the minor characters in Finding Nemo.

Finding Nemo

Gurgle: "She wouldn't stop shaking the bag."
Bubbles: "Poor Chuckles."
Deb: "He was her present last year."
Bloat: "Hitched a ride on the porcelain express."
Peach: She's a fish killer."
Bubbles, Gurgle, Peach, Deb and Bloat, about Chuckles

In Finding Nemo, Chuckles was a goldfish who was only seen in a picture. He was a pet for Darla, but he sadly died because Darla wouldn't stop shaking the bag he was in.

Before he was handed over to Darla, he could have been a member of the Tank Gang, as Bubbles, Deb, and Bloat were mourning over Chuckles's death.