Pearsei are smart fish. I tell this story as an example. When my pearsei was young it was very sick and I decided to do a treatment that involved catching her and pumping a medicine/food mix into her stomach. Treatment went for about a week and it went well and she got better.
So after all this, one day I approach the tank and she goes and hides in the back behind the large mopaniwood. Every time she saw me she would hide. I had to test this out and see if it was just me. I had my wife come up to the tank multiple times with me out of sight and sure enough the pearsei came out and interacted and begged for food. With me she would hide.
The pearsei had associated me with something bad and remembered it. Took about two weeks for her to come around but eventually her stomach got the best of her.