Personalities in a crowd: What shapes the behaviour of Eurasian perch and other shoaling fishes?

Lately, there has been an increasing interest in intraspecific variation in behaviour, and numerous studies on persona- lity have been performed in a variety of animals, including several fish species. Individuals have been divided into coping style categories or arranged along a behaviour gradient, such as the bold/shy continuum. However, many fish species live in groups, and the social environment can influence the behaviour of an animal in different ways. There may be conflicts within groups due to competition for resources, and dominance hierarchies are commonly found. On the other hand, there are many benefits of con- sensus decision-making within the group. Conformity of behaviour is probably adaptive, due to the benefit of public information on, for example, food resources and predation risk. Accordingly, studies of fish shoals have found evidence of consensus deci- sion-making. Furthermore, factors in the environment, such as predation risk would also influence the behaviour expressed. To be able to understand behaviour patterns in a group of fish, it is necessary to consider the variation of individual characteristics, and how the group, as well as other environmental factors, affects the behaviour of individuals. Here, I will review studies on different aspects of personality within a social context in fish, with a special emphasis on the Eurasian perch Perca fluviatilis (Current Zo- ology 58 (1): 35-44, 2012).