They actually proved that goldfish have at least a week long memory, instead of the widely accepted 3 second memory. I thought it was complete bull from the start.
My oscars recognize virtually anyone who is around the tank frequently, or even if they only come here once in a while. They put out a different response to each person, and my cousin Riley and I get the best ones, they are like dogs wagging tails when one of us are around. When i only are around, they will even be trained. I have actually trained them using freeze dried krill, but when that ran out, they got mad at me.
Oscars have even been observed watching tv. If i make my pair angry, they will hold a grudge for about a week, and then they begin to get over it. Fish, who are often thought to be stupid or brutish, are actually very smart. Some, such as oscars and triggerfish, can even give dogs and cats a run for their money. With the fish often coming out on top. Never underestimate a fish.
My fish can recognize food as well. The oscars, if they find they like a certain food, will only get excited if they see that particular can, and can differentiate between bags of the same shape, going for the colour they have found to be delicous. Also, they dont even have to see the can before getting excited, if they see my arm reaching for the food, they go bananas. However, if it is a can of food they dont like, they look at me like im a freak, lose their excitement, and swim away slowly. Fun!
-Lynden
P.S., the reason your discus do not behave personably is because discus are timid, and not very affectionate.