Maybe it's just me, but I don't think it's cruel to put some shrimp or a ADF or something in a 1gal. My ADF breathes from the surface, so no worries about oxygenating the water, although I still may give him a filter or pump of some sort, he has PLENTY of room to swim, he seems to be happy, I see no reason it would be considered cruel, maybe if you put a school of tetras in a 1gal, that would be cruel.