The aquatic environment of fish can vary over developmental and evolutionary time scales, eliciting responses at levels of organization ranging from the gene to the whole-animal (Johnston and Wilson, 2006). Temperature and environmental variables such as oxygen availability, pH, salinity, pollution and turbidity can directly and/or indirectly influence physiological processes and behaviour in fish (Bennett, 1990; Prosser, 1991). Many of these factors, 270such incidences of hypoxia and pollution, are also becoming more commonplace in coastal areas, and can have profound effects on fish swimming behavior (Domenici et al., 2007a). Although numerous studies have successfully elucidated the functional consequences of environmental variation on locomotion, and their underlying mechanisms, the link between such variation and fitness is not often established (Garland and Carter, 1994; Irschick and Garland, 2001; Wilson, 2005). In this context, studies of prey capture/escape success and reproductive performance are also likely to be of direct relevance.