Abstract

Among the many benefits associated with group-living in animals is a potentially reduced cost of locomotion for individual group members. Fish schools are a prime example in which individuals can exploit zones of low pressure or vortices created by school mates to increase their own efficiency of movement. Here I first discuss work with mullet and mackerel, demonstrating how differences in energy expenditure by fish in different positions within a school can influence trade-offs associated with spatial positioning and school membership. In particular, it seems that the physiological traits of individual fish may affect their preferred position within a group in response to energetic trade-offs. Interestingly, however, even fish swimming toward the front of a group, or at least ahead of the neighbours, are able to gain an energetic advantage over swimming in isolation. Overall, trade-offs of energetic efficiency experienced by fish in schools may interact with other trade-offs associated with spatial positions, such as those related to predator-avoidance or foraging, to affect overall group structure.