I believe I saw the doomsday preppers episode. He had chickens above the pool, which provided droppings/for the fish, and the fish water was basically fertilizer and fed a garden or something like that. It may not have been that episode, but I did see something like this on a show.
Seems like chickens and a garden are less hassle. The rabbits, although useful for providing fertilizer, were far too high maintenance. They produced much more offspring than I could get rid of fast enough. Not worth the hassle, and the meat needs to be prepared in a slow cooker type meal to be soft like chicken, otherwise it is a bit gamey (it does not BBQ well, unless it's really young maybe).