What is the memory span of a fish

That blank look in the eyes of a fish may not be evidence of a three-second memory span after all; it might be clockwatching.

Research has shown that far from being forgetful, fish can learn to tell the time.

Phil Gee, a psychologist from Plymouth University, made the findings by training fish to collect food at certain times of day. Initially the fish were taught to press a small lever in their bowl to get their food. When they had mastered this, Mr Gee's research team restricted the availability of the food until it was dispensed for just one hour in the day.

"The fish worked out that if they hit the lever around that time, they would get food," Mr Gee said. "Their activity around the lever increased enormously just before the set hour when their food was dispensed. But then if no food came out, they stopped pressing the lever when the hour was up.

"It shows that they are probably able to adapt to changes in their circumstances, like any other small animals and birds. It tells us that they are able to learn."

Mr Gee said scientists had known for some time that that fish - even goldfish - have more than a three-second memory and can remember things for up to three months. They can also learn to distinguish between different shapes, colours and sounds.

It is hoped the discovery that they can sense timing could benefit fish farmers in the developing world, enabling them to control their stocks without expensive equipment.