Can you keep saltwater fish in a 5 gallon? I know you can with certain small freshwater fish, but I'm not sure if different rules apply to saltwater.

I'll let someone else answer the fish question because I'm not 100% on that.

But I think inverts are best suited for that size tank, instead of fish. Sexy shrimps are incredible! I'd love a nano tank with just some sexy shrimps and maybe anemones for their host.