In a study published this week in PNAS, researchers at the mathematics institute in Uppsala, working together with biologists in Sydney, have studied groups of a small lake-dwelling fish, known as the mosquito fish. By tracking the fish using computer imaging and fitting mathematical models to how the fish interact with each other, the researchers were able to decode the rules by which these fish interact with each other. The rules turned out to be strikingly simple but effective. Fish try to catch up with other fish in front of them, but they slow down when they get too close. Much in the same way as car drivers on an open highway try to keep a fixed distance from each other. Fish also turn their bodies to move towards their neighbors and appear to react primarily to only their nearest neighbor. Through these simple rules, shoals of mosquito fish move in a co-ordinated fashion.