Fish tank with no light and heat?

[AdamJB]

I've been keeping a 62 litre fish tank for several months and I've really loved it. But after I saw how people keep fish without filters and heaters, is it really possible to have a small fishtank with no filter or heat, or any electricity input, and the fish be healthy?

I know people do these a lot in fishbowls, but are the fish really okay in them? I just think it would be really nice to have a small tank here on my desk which would really keep my office theme going, but it would be too difficult to have any filters going in it, a light would be possible but I don't know of any filters that are small enough for the kind of thing I'm thinking. I thought I should check here with people who know what they're doing, because I don't!

Sorry if this question is a straight up and obvious no in your eyes, but I just had the idea and I thought it would be really neat to have some tiny fish swimming around for me to watch.