Anyone who's had a goldfish knows that when they lift the top to feed, the fish will rise to get the first mouthful. This needs memory to associate the lifting of the top with food.
I always understood that goldfish had a memory of 3 seconds, but the ones in my pond blinking well know when I am approaching with food!!! Greedy sods.
I heard that when a goldfish swims round it's bowl & sees an ornamental bridge it thinks 'oh that's nice , haven't seen that there before'...................................'oh that's nice , haven't seen that there before' ..................................'oh that's nice...
Ironic, don't you think, that goldfish appear to remember stuff after 3 months - but members here can only have a vague recollection that they "read or heard somewhere" about this...