Research by biologists has revealed that some species of fish display personality traits.
Scientists believe a strong personality is important for survival
Fish are influenced by watching the behaviour of other fish, said experts from the University of Liverpool.
Experiments on rainbow trout showed that "bold" fish became more wary after being with "shy" fish, but the reverse did not happen.
Scientists believe that a strong personality may help in the evolution of a species.
The research team from the university's Biological Sciences department put toy bricks in the tank to create a fear response in the trout.
They found that bold fish approached the object within a few minutes whereas shy fish took more than ten minutes to approach.
"Bold fish who observed the way shy fish reacted to the Lego objects became much more cautious in their behaviour," said Dr Lynne Sneddon.
"In contrast, shy fish who observed bold fish did not alter their behaviour - they remained just as shy as before," she continued.
The experts also found that the more time bold and shy fish spent watching each other the more their behaviour changed.