Hidden depths of goldfish

But it seems that goldfish are not as gormless as they look.

Far from having a memory span of only a few seconds, as is commonly believed, goldfish can actually remember things for at least three months.

Not only that, they can be trained to push levers at a certain time of the day to get food, putting them on a par with birds and small mammals.

The remarkable findings were made by researchers at Plymouth University. Psychologist Dr Philip Gee installed a food dispenser attached to a lever in a tank of five goldfish.

When the fish nudged the lever food was released into the water. The goldfish soon learned to push the lever when they were hungry.

But as the three-month experiment progressed, Dr Gee made things a little more complicated. He adjusted the lever so that it would work only during one hour each day. The goldfish adapted to the new routine and would nudge the lever far less during the hours that it did not dispense food.

But as the feeding hour approached, they would gather around the lever, having apparently remembered that it was nearly lunchtime.

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

The discovery has implications for communities in developing countries which depend on marine life for food. Previous research has found that fish such as cod and trout can be attracted to feeding areas by pulses of sound transmitted through the water.

Fish farmers often use the technology to harvest their stock and monitor their condition. But many poor communities cannot afford the equipment needed for this method.

'Hopefully it would be a more efficient way of harvesting fish than the way it is done now, especially for poorer people,' said Dr Gee.