About Freshwater Fishes

There are currently 18,380 recognised freshwater fishes. This is 51% of all the world’s known fish species, and one quarter of all known vertebrates on earth.  A remarkable fact given that only 1% of earths surface area is comprised of freshwater, making freshwater ecosystems hotspots of biodiversity.

Infographic. On the left is a globe with the caption: 1% of Aquatic Habitats is Freshwater. On the right is a circle filled with fish silhouettes, the upper half of the circle being bolded and the lower half greyed out, with the caption 51% of Known Fish Species are found in Freshwater.

Freshwater fishes are extremely diverse. They include some of the smallest vertebrates on earth, such as the minnow, Paedocypris progenetica, that lives in peat swamps in Indonesia and is just 8mm long and weighs in at 0.004g, and giant fish such as the Mekong giant catfish, Pangasianodon gigas, Mekong giant freshwater stingray, Himantura chaophraya, and beluga sturgeon, Huso huso, all of which can reach more than 3m in length and weigh more than more than 300kg.

What are Freshwater Fish? Freshwater fishes are species that live in freshwater or brackish water. It also includes species that need freshwater for a critical part of their life cycle. This includes: all salt intolerant (stenohaline) species such as carps, characins and cichlids; salt tolerant (euryhaline) species such as salmon, eels, some rays, sturgeon and sawfish; some estuarine species such as archer fish and gobies; and soda and salt lake fish. It excludes waif migrants, or coral reef species that spawn in mangroves, and fish that live in the ocean in freshwater lenses.

While diverse at the species level, freshwater fishes are less diverse at higher taxonomic levels that marine fishes. Almost 90% of freshwater fish species are found in just eight orders: carps, minnows and loaches (Cypriniformes), catfishes (Siluriformes),characins and tetras (Characiformes), cichlids (Cichliformes), toothcarps and killifishes (Cyprinodontiformes), gobies (Gobiiformes), perch-like fishes (Perciformes), and bettas and gouramis (Anabantiformes).

species in that order. A quarter of the piee is Carps, minnows and loaches, and another quarter is Catfishes, with the other six orders make up the remaining half of the pie.

In addition to being hotspots for biodiversity, freshwater ecosystems around the world are hotspots for biodiversity imperilment, with populations of freshwater species having declined at twice the rate of biodiversity in marine and terrestrial realms (LPI, 2022).  Around one third of freshwater fish species are threatened with extinction, and 80 species have already been declared Extinct. Populations of migratory fishes have declined by 76 per cent since 1970, and populations of large iconic fish like the beluga sturgeon and the Mekong giant catfish, have declined by 94% since 1970.

Number of freshwater fish species in each IUCN Red List Category, from a total of 10516 assessed species. Extinct: 80. Extinct in the Wild: 10. Critically Endangered: 583, of which 115 are presumed extinct. Endangered: 870. Vulnerable: 966. Near Threatened: 511. Least Concern: 5332. Data Deficient: 264.

Freshwater ecosystems face a number of threats around the world. This includes habitat loss, pollution from agricultural, urban and industrial sources, over-abstraction of water, over-exploitation of resources and illegal trade in species, the introduction of invasive non-native species, and the loss of free-flowing rivers due to hydropower and infrastructure development.

For more information about the diversity of freshwater fishes and the threats facing freshwater fishes and what can be done to help, please see World’s Forgotten Fishes (https://wwf.panda.org/discover/our_focus/freshwater_practice/the_world_s_forgotten_fishes/).