The traditional view that fish not have the brain power to retain memories is "absolute rubbish" said Dr Kevin Warburton, an accessory researcher with Charles Sturt University's Institute for Land, Water and Society in Australia.

He made his conclusion after studying the performance of Australian freshwater fish such as the silver perch, which can remember a predator for numerous months after only one encounter.
Dr Warburton said: "Fish are quite complicated."Fish can keep in mind prey types for months. They can become skilled to avoid predators after being attacked once and they retain this memory for several months.

"And carp that have been caught by fishers keep away from hooks for at least a year."That fish have only a three second memory is just trash." Nobody knows where the three-second fable comes from.

Dr Ashley Ward, a fish biologist at Sydney University, said: "It seems to come from an advert many years previously, but no one is sure what it was for." Fish can also learn to progress how to catch food, said Dr Warburton, carry out acts of trickery and modify their behavior.

For example, in reef environments cleaner fish who eat vermin off 'client' fish act on best behavior when they spot a larger patron. Dr Warburton said: "What's interesting is that they co-operate more with clients when they are being observed by other potential clients. "This improves their 'image' and their probability of attracting clients.

"Some cleaners help with small clients to raise their image so as to deceive larger clients, which they then cheat on by stinging them rather than removing their parasites."