"Freshwater fishes" are species that lives all, or a critical part of its life in either freshwater inland or brackish estuaries. This definition includes: all "primary" (salt intolerant or stenohaline) freshwater fish, e.g. carps, characins, cichlids; all "secondary" (salt tolerant or euryhaline) freshwater fish, e.g. salmon, eels, some rays and sawfish (elasmobranchs); some estuarine fish, e.g. archer fish and gobies; and soda and salt lake fish. This definition excludes: coral reef fish that spawn in mangroves, occasional "waif migrants" from the sea into freshwater; and fish in the sea in "freshwater lenses".
It has been estimated that the total number of all fishes is 32,500 species (Nelson, 2006). Considering that freshwater may constitute less than 0.3% of available global water, it is remarkable that there are more than 15,000 freshwater fish species. While marine communities contain more species in total, freshwaters are far richer per unit volume of habitat. Here, freshwater fish species occur at one per 15 km¬≥ of water (cf. one per 100,000 km¬≥ of sea water). This reflects the productivity, physiographic diversity and geographical isolation of freshwater habitats (Ormerod, 2003). Comprising approximately 25% of all vertebrates, freshwater fishes are an important component of global biodiversity (Reid et al., 2013).
Approximately 7,956 of all fish species (30%) are contained within just 6 of the 515 taxonomic families. Remarkably, ca 6,100 (77%) of species in these representative families live in freshwater (Figure 1).
Much taxonomic work still remains to be done and our knowledge on fishes changes rapidly. Since 1976, an average of 305 fish species have been described as new to science per year (Reid et al., 2013).
arowanas of tropical rainforest habitats.
Searchable online, electronic databases and catalogues, such as California Academy of Sciences: Catalog of Fishes, FishBase and Wikispecies, are excellent resources; providing data, images and scientific literature on fish species and subspecies.
Nelson J.S. 2006. Fishes of the world. Fourth Edition. John Wiley & Sons.
Ormerod S.J. 2003. Current issues with fish and fisheries: editor"s overview and introduction. Journal of Applied Ecology. 40:, 204‚Äì213. Available here
Reid, G. McG., Contreras MacBeath, T. and Csatadi, K. 2013. Global challenges in freshwater fish conservation related to public aquariums and the aquarium industry. International Zoo Yearbook 47(1): 6-45. Available here