Re: Do gold fish have memory?

The short answer to your question is yes.

This type of learning behavior you describe is traditionally called 
"classical conditioning".  In classical conditioning, an organism 
associates particular stimulus (like food) with an intrinsically unrelated 
stimulus, like tank-tapping.  Many types of animals are capable of this 
behavior, such as mammals, bony fish (like goldfish), and maybe even some 
insects.