There have been a few scientific studies trying to determine the memory length of fish, it has been argued that goldfish, well known to be the stupidest fish on the planet, have a memory span of 3 seconds ( See "Finding Nemo" the movie

) and some people including PETA got so pissed off about that they paid scientist to prove goldfish have longer memories than 3 seconds. Those scientists "proved" goldfish had a memory span of "at least" 3 months. 3 seconds, 3 months, whatever. Still pretty stupid. Mythbusters did a TV show on the myth, they "proved goldfish had a memory span of 8 seconds or more. B.F.D. if you ask me. Sticklebacks--- really stupid, no proof they have any memory span at all. Dr. Jens Krause, from Leeds University did a study I will try to find in one of my computers that fish are smarter than we think they are, but still only could come up with memory spans of less than 20 weeks. I have the study on my laptop, but it needs to get repaired before I can charge it again

and retrieve the study, but here is the abstract
http://www....edu/~icouzin/Hensor.htm
Just NEVER loan your car keys to a fish!!!