Familiarity in schooling fish: How long does it take to acquire?

Previous work has demonstrated that fish prefer to school with familiar individuals. In this study schooling preferences for familiar female guppies, Poecilia reticulata, developed gradually over 12 days, but once established were maintained. This contrasts with condition-dependent recognition in which fish rapidly learn to discriminate between conspecifics on the basis of obvious morphological differences such as body size. (C) 1997 The Association for the Study of Animal Behaviour.