In this study, goldfish were trained to associate a light with an electric shock. The researchers found that the fish would remember this association for up to three seconds, after which they would forget it.
However, subsequent research has shown that goldfish actually have a much longer memory than three seconds. In fact, they can remember tasks for up to five months.
The three-second memory myth is likely due to the fact that goldfish have a very short attention span. They are easily distracted and can quickly forget what they are doing if they are interrupted.
Additionally, goldfish have a small brain, which means that they can only store a limited amount of information at a time.