If you're in a goldfish I think you're already out of luck

> Who gets rich in a goldfish

I think it must be the diver because he found the treasure chest, assuming that it isn't counterfeit:

https://www.amazon.com/Bestgoo-Aquarium-Ornament-Live-Action...

Historically, the people who got rich during the gold rush were the ones offering services and selling goods to the miners.

So the answer to your question is the latter.