This Goldeen is a Water-type Pokémon owned by Misty.
It still resides with her in the Cerulean Gym. It is one of Misty's favorite Pokémon. Its first appearance was in Pokemon Emergency!, when it was used to distract Team Rocket. Since Goldeen couldn't manage on land, it flopped around. Team Rocket looked confused before Misty called it back to its Poké Ball, saying she was just "warming up".
Goldeen hasn't been sent to battle much in the series, but has shown to be a valuable asset when it came to swimming passengers through the water and locating something within the water.