Patterns in Freshwater Fish Diversity

This chapter provides a brief overview of freshwater fish diversity globally, the factors underlying diversity patterns among and within river basins and phylogenetic groups, and the main threats to this diversity in the Anthropocene. Continental freshwaters represent among the most diverse and species-dense habitats on Earth, with almost 18,000 fish species (>50% of all fish species) compressed into just <0.5% of the total surface area, and a miniscule (<0.01%) proportion of the planetary water supply. Freshwater fish diversity reaches a peak in the large lowland tropical river basins, in particular in the Amazon, Congo and Mekong basins. At an intercontinental scale, variability of freshwater fish species richness is related to the total volume and heterogeneity of aquatic habitats, and the stability of these environments over evolutionary time scales. Regional fish species richness, species composition, and functional traits all change predictably along environmental gradients from headwater to estuary (the river continuum concept). In most parts of the world, the abundance and diversity of riverine fishes is strongly related to the regular exchange of nutrients and organic matter associated with adjacent floodplains (the flood pulse concept). Freshwater fishes currently face a multitude of threats in all parts of the world, which will lead to severe losses in abundance and diversity in the absence of concerted conservation actions.