What kind of fish can you put in a 2 gallon fish tank?

Nothing, if you want to be humane. Goldfish take at least 10 gallons each fish because of how much waste they produce. Most fish are the same.

but there is one fish a betta i had mine in a 1 gallon tank for 3 years and its been fine the only thing is that you have to clean it out every 3 weeks.