A key question in ecology is how biological diversity affects ecosystem functioning.This is of particular importance in the general context of human activities that have impacts on biodiversity,ecosystems,and their complex relationship.Currently,community functional diversity is receiving considerable academic attention,and is considered important in solving ecological problems.However,research has mostly focused on plant or microbial communities,and there has been almost no related research into fish communities.Although freshwater ecosystems represent only a very small part of the planet (<1% of Earth's surface),they support a disproportionally rich diversity of biological life and provide countless ecological services to humans (most notably to urban populations),including water purification,drinking water,food production,and leisure activities.For assemblages like reef fish communities,human disturbances such as fishing (i.e.the removal of target specimens) could reduce functional diversity and potentially have significant effects on ecosystem functioning.Fishery resources in China are declining because of many human-induced stressors such as overfishing,dam construction,and biological invasions,and aquatic ecosystem function has therefore undergone a serious decline.It has been suggested that the most appropriate way to fully understand and quantify the effects of natural-and human-induced perturbations on biodiversity is to apply functional approaches,as these incorporate the interactions between organisms and their surrounding environment.Functional diversity can be defined as the value,range,distribution,and ecological importance of organisms' functional attributes in a community.However,empirical assessments of the potential responses of freshwater functional diversity patterns to human-induced perturbations are still lacking.We reviewed the functional diversity of freshwater fish and methods of its calculation,including data acquisition and analysis,to provide a new theoretical basis for the protection of fish resources.Three independent indices have been proposed to quantify functional diversity of freshwater fishes:functional richness (FRic),functional evenness (FEve),and functional divergence (FDiv).These are based on the distribution of species and their abundance in a multidimensional Euclidean space (i.e.the so-called functional space) created using many functional traits of species.No clear criteria exist that define the most suitable index to investigate functional diversity.Increasing number of ecologists have been using a combination of several multi-trait indices to quantify functional diversity,since the use of complementary functional diversity indices can provide a better understanding of the role of biodiversity in ecosystem functioning.