OP please please stop asking about putting fish into tiny tanks, I'm not an expert by any means but a 4 gallon tank isn't big enough for anything other than shrimp if we're being realistic. There's been a number of threads of a similar nature asking what fish you can fit into obscenely small tanks. I'm not sure if there's a limit to how much space you have but please remember these are living beings and we have a responsibility to house them appropriately and ensure their needs are met, which isn't going to happen in 2, 3 or 4 gallon tanks. This isn't a personal attack, it won't be pleasant for you or the fish if you put them in such a tank as they'll be dead within a matter of weeks because of the unsuitable living conditions.