what makes you so sure that your fish wouldn't be able to grasp the situation? Put it this way, if you walked by your tank, and every time you did you chased your fish around the tank violently with a net, i would give it about 3 days until they hid when they saw you. which in fact shows that they can learn and even recognize YOU from someone else. If they can show this level of thinking i wouldn't put it past them to have some type of emotions either, such as happiness and sadness, anger, and being comfortable. why do you think it takes such a long time for piranha to come out of there shell? probably because they are scared (which is another emotion) and need to become more familiar and at ease in a particular tank.. with that said, cramping your fish will leave them unhappy and stressed out, bad water quality leads to disease and a whole bunch of other problems... Not showing good colors and sickness are common side effects and your case will be no exception..
Thanks Joe, exactly what i was trying to say