Here fish are simulated in a flow field – the tiny white bubbles are designed to show how the currents are moving in two Von Karman streets behind two circular obstructions. each fish looks at its nearest 3 neighbours and moderates its direction of travel based on three possibilities 1. Too close – move away, 2. Just right – move parallel and 3. Too far – move towards. Then the speed of travel is moderated to move slowly across the flow field from right to left. The model is coded in MATLAB.

The point of the model is to consider the trade off a fish might make between staying in a group and working harder in chaotic currents. The fishes’ tails change length in proportion to how hard they are working to keep up, and their heads change colour, red – working hard, orange – working medium, and green – taking it easy.