From Fortean Times:
Ichthyologists have known for a long time that this isn't true, and in
2003 Dr Phil Gee, of the School of Psychology at the University of
Plymouth, published research which blew it out of the water. Goldfish
have a memory span of at least three months, and can distinguish
between different shapes, colours and sounds.
In the Plymouth experiments, goldfish were trained to press a lever to
gain a food reward; when the lever was fixed to work only for an hour
a day, the fish soon learned to activate it at the correct time.
The MythBusters have tested this also (watch the video):
Jamie trained his goldfish to recognize color patterns and complete an
obstacle course under water.
They remembered what Jamie had taught
them over a month later and easily completed the same course without
(from MythBusters Results)
From ABC News (2008):
... a 15-year-old schoolboy from Adelaide has just debunked the theory.
Rory Stokes (a student at the Australian Science and Mathematics School) conducted a school experiment to prove his theory, using a small
tank of goldfish.
"I decided to get a bit of red Lego and just feed them next to that.
Every day I'd put it in and sprinkle food around it," he said.
"At first they were a bit scared of it, a bit wary, but by the end of
the three weeks, they were actually almost coming before I put the
After leaving the fish alone for a week, Rory placed the red Lego
block in the tank again.
"They remembered perfectly well," he said.