The Giant Goldfish make their appearance in the episode "Evicted!," in which Marceline claims to have ridden one.
Appearance
They look like regular goldfish, but they are almost as large as whales. Some of them are red instead of gold. Their mouths are significantly oversized, bearing a closer resemblance to carp's or koi's mouths than to normal goldfish's.
Gallery
Giant Goldfish modelsheet
Marceline riding the Giant Goldfish
