Hey, im not sure if this has been posted yet, if it has disregard this post.
I knew this was true before reading it and ive only had my tilapia for 1 week. They are very intricate, and not simple as some may think. If you just watch the fish very closely you can see they remember things way longer than the common belief of "3 seconds". Just by watching you can see how they interact on a level that would require thoughts to last much longer and 3 seconds.
Never underestimate the complexity of anything that is in existence and its interactions with other things.
My favorite quote: " True knowledge is knowing that you know nothing" ~Socrates~
If fish had only a 3 second memory, why would they require regular set feeding times. My fish definitely get used to particular feeding times and if I show up and toss food in at an odd time it takes them a bit to realize there are treats there but at the regular time for the feeder to go off, they are up there waiting for it.
and Heck, have you ever seen the videos where people have trained their goldfish? You can't train an animal that doesn't remember.