Mr. Goldfish is always happy

No, they actually don't. It's a common misconception. Studies show that they actually have a memory of about 3 months.

Was going to say that. It was a fallacy created by pet shops to sell tiny tanks, without the owner feeling guilty.
Studies were conducted using slides with coloured circles in them, when the scientists moved the slides/upended them, the goldfish would go to the exact spots it had just come from at the end of the maze.