The purpose of this thesis is to investigate the dynamics of a school of fish and design a controller to help steer the fish. Many species of fish can only live in waters of a certain temperature and will need to migrate from time to time in order to find an area with suitable temperature. The controller is designed to guide the fish as a group to an area of desired temperature. This is done in a bottom-up approach, starting from basics and explaining each part of the controller and why it is necessary. The model is non-linear and cannot easily be solved analytically, therefore it is discretized and solved numerically in Matlab. Simulations then compare the behaviour of the fish for different isotherms