The study - by scientists at the University of Exeter and Texas A and M University - found that small fish were able to do well in contests for food against larger fish if they were aggressive.
Dr Alastair Wilson from Biosciences at the University of Exeter said that their research suggests that personality can have far reaching implications for life and survival.
In the study, the sheepshead swordtail fish (Xiphophorus birchmanni) fish were placed in pairs in a fish tank, food was added and their behaviour was captured on film.
The feeding contest trials were carried out with both male and female fish and the researchers found that while males regularly attacked their opponent to win the food, females were much less aggressive and rarely attacked.
The study has been published in the journal Behavioral Ecology and Sociobiology