Fish only have a 3-second memory?

I always thought that was true, but apparently fish can remember up to 3 months (From The Fortean Times):

The myth
Goldfish have a three-second (or seven-second) memory span.

The "truth"
Keeping a fish in a small bowl is clearly an act of monstrous cruelty, and so a myth has arisen which allows pet owners to feel less guilty: that fish - in most versions, specifically goldfish - can't remember anything which happened more than a few seconds ago, and therefore never get bored with their tiny homes. (The precise number of seconds varies, but is generally seven or three - as usual in matters mythconceptional).

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. Fish 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. A number of studies have shown that farmed fish can easily be trained to feed at particular times and places, in response to an audible signal.