Fresh waters harbour exceptional levels of biodiversity (Chapter 1). However, various anthropogenic environmental forces threaten this splendid richness (Carpenter et al., 1992; Dudgeon et al., 2006; Strayer & Dudgeon, 2010; Chapter 2). These threats include invasive species (Rahel & Olden, 2008; Chapter 8), land-use changes (Allan, 2004), decreased connectivity (Jackson et al., 2001; Chapter 10) and various changes to water quantity and quality (Malmqvist & Rundle, 2002; Chapters 4–6). Furthermore, global climate change has been increasingly recognised as a pressing environmental change affecting many other stressors as well as having direct effects on fish diversity (Tonn, 1990; Comte et al., 2013). Climate change affects fish individuals, populations, species and communities at various spatial and temporal scales (Tonn, 1990; Carpenter et al., 1992; Graham & Harrod, 2009), ranging from effects on the behaviour of fish at a local scale to species distributions at biogeographic scales (Chu et al., 2005; Hickling et al., 2006; Ficke et al., 2007; Hein et al., 2011; Markovic et al., 2012).
Although climates have changed throughout the history of the Earth, the current rates of increases in temperature, changes in rainfall and occurrence of exceptional weather conditions are unprecedented (IPCC, 2007). For example, global annual average air temperatures are, depending on a climate change scenario, projected to increase from 1°C to 5°C by the end of this century, with much among-region variation. Highest changes in temperature have been seen and are likely to be recorded at high latitudes (IPCC, 2007), where the effects of increased water temperature on fish are also likely to be most profound (Lehtonen, 1996; Chu et al., 2005; Sharma et al., 2007; Heino et al., 2009). By contrast, closer to the equator, changes in temperature are not likely to be that pronounced, but changes in rainfall, decreases in river discharge and increases in human water withdrawal are likely to increase in the future (Xenopoulos et al., 2005; Thieme et al., 2010). Such changes suggest that there may be more irregular droughts and floods, which affect fish at various levels of organisation from individual physiology and population abundance to community structure and range shifts (Graham & Harrod, 2009; Morrongiello et al., 2011). Predicting the effects of climate change on the abundance and distribution of fish is thus highly challenging and regionally variable, but important for the conservation of fish diversity (Cochrane et al., 2009; Comte et al., 2013).