Development of early social behaviour of rainbow trout, Salmo Gairdneri (Pisces, Salmonidae)

Young rainbow trout do not begin agonistic behaviour until they are free-swimming. Agonistic behaviour initially consists mostly of simple, straightforward attacks. More complex threat patterns are added with increasing age. Increased water flow rate promotes station-holding and apparently territorial behaviour, especially at low fish densities. High fish densities lead to an increase in agonistic interactions, especially in fast flowing water. The interplay of these factors with the developmental processes of social behaviour is discussed.