I dont understand, what is the experiment. You dont think people have had numerous cariba in a tank before? I dont think cariba need any more space than any other pygo. Mine dont take up any more room than my reds that are the same size. The larger cariba take more room, but so does the larger nattereri. The larger the pygo the larger the territory they claim.
People have been keeping piranhas for a long time, I doubt we are doing anything that has not already been done or tried many times before.