Probably the reason that most fish do not have memories.
The Perfish is a highly vindictive fish, it remember all that ever happens to it and it's family and will seek revenge for any bad deeds towards it.

It is said that fishers who have caught a Perfish can never fish in the same waters again. When cuaght and out of the water the perfish will virabrate it's four fins - one on each side, one on top and one on bottom - so fast that it creates such a painful buzzing noise that it has to be thrown back in to stop it. Then if that same fisher comes back to that spot it will deleberatly let itself become caught so that it can inflict more pain on it's enemy.

One of the few creatures that can catch the Perfish is the Finbear. Over the years of evolution the Finbear has learnt to cope with the defense tactics of the Perfish, most probably because it is one of the few things it has to eat it has had to learn.