SELFORGANIZATION OF FISH SCHOOLS - AN OBJECT-ORIENTED MODEL

Simulation models help to understand how individual interactions can lead to selforganization of large, moving polarized schools of fish. To some extend the underlying mechanisms in these models are still hypothetical. This paper investigates and confirms previously published results and suggests an alternative model. Previous models of fish schools used the assumption that individuals modify their swimming direction and speed as a reaction to a small fixed number of other individuals swimming closest to their own swimming direction (front priority). They also used discrete transitions between different reaction types to their neighbours (see Huth and Wissel, this volume). These models are able to simulate school movement in a homogeneous environment but fail under certain heterogeneous conditions (e.g. when schools meet obstacles) and do not adequately simulate the formation process of schools. We present an alternative model, in which a fish's new speed and swimming direction is influenced by all visible neighbours. Each neighbour contributes a vector component weighted according to its distance. These components are aggregated to determine to what extent the different behavioural modes of searching, attraction, parallel orientation and repulsion contribute to a modification of an individual's movement in a particular situation. The resulting model reproduces schooling behaviour, organization of schools and has fewer artificial requirements concerning a biological interpretation of the underlying mechanisms. It shows how a comparison of different modelling approaches, empirical observation of inter-organismic interaction, and physiological research can stimulate each other in order to understand a complex, dynamic phenomenon.