racinghamster is right. The water conditions is what you'll basically be taking care of, the fish are just there for you to watch and enjoy. It's like you need to build an entire habitat for fish, where as with other pets it's not to that extent, as you can't really bring semi-desert into a hamster habitat, though you can make it look like one.
Fish tanks need to be cycled without any fish in the tank for about 1 month before you get the fish. This is so you can test the water and make sure the levels of nitrate and nitrite are at 0 (I think, haven't been researching fish for a while) and that the PH suits the fish you want to buy.
Minnows need a tank of at least 2ft x 1ft at absolute minimum for a group of 6. That's the least I'd say you can have in a group, they do much better in about a group of 8 - 12. They're also lovely to watch when there's a lot of them, and the males 'dance' together to compete for females and display their red fins. It's lovely. They like habitats with a moderate amount of plants and some hiding places. especially if the females want to have a rest from the males bothering them. I can give you more information if you're interested in minnows, I'd love to get some again but my hamsters take up all the room I have now! haha
