I have started to do this. There is this little private store that sells exotic fish. My local petsmart carries some semi-rare fish and/or fish that can be used to be grown bigger and restold for a pretty reasonable price. They started stocking dragon gobies almost all year round now. They come in at 7''-8'' for $5. I also do fish that are seen everyday like oscars, red devils, four lined pims, and knifes. Obviously I don't do all of these at once. I do enjoy keeping them while they are growing and observing their behavior. At the same time it helps me save a little more money for the hobby. Tell me what you guys keep?