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Why do sources give different totals?
“Freshwater fish” does not always mean a fish that spends its entire life in freshwater. The 2025 CMS assessment uses a broad definition: a species counts if it spends some or all of its life in fresh water. That can include fish that also use brackish or marine water, including migratory species that move between rivers and the sea.
The IUCN/SSC Freshwater Fish Specialist Group likewise includes fish living in fresh or brackish water, or those that need freshwater for a critical part of their life cycle. Its stated exclusions include occasional “waif” migrants, coral-reef fish that spawn in mangroves, and fish living in freshwater lenses in the ocean.
FishBase uses a different set of categories. Its June 2026 table puts freshwater and brackish-water fish in a freshwater category, but lists diadromous fish separately. The different totals therefore reflect category boundaries and taxonomic treatment, not necessarily a disagreement about the same precisely defined set of species.
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- Bright Cardinal Tetra Live Fish: Add vibrant blue and red color to your freshwater aquarium with Cardinal Tetras, a classic tropical schooling fish loved for planted and community tanks
- Peaceful Community Aquarium Fish: Cardinal Tetras are calm, active swimmers that pair well with other small peaceful species in properly maintained freshwater aquariums
- Compatible with Community Tanks: Suitable for peaceful freshwater setups with other small, non-aggressive fish such as rasboras, small tetras, corydoras, and other gentle tank mates
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| Source and date | Reported count | What the figure represents |
|---|---|---|
| Eschmeyer’s Catalog of Fishes, as reported by the 2025 CMS assessment | 19,013 | Valid freshwater fish species |
| IUCN/SSC Freshwater Fish Specialist Group, as reported by the 2025 CMS assessment | 18,898 | Recognized freshwater fish species |
| FishBase, June 2026 | 17,817 | FishBase freshwater category, including freshwater/brackish and freshwater-only fish; diadromous fish are categorized separately |
What counts as a freshwater fish?
Some species are freshwater specialists; others move between habitats or use different salinities at different life stages. Anadromous fish migrate from the sea into freshwater to reproduce, while catadromous fish make the reverse journey; amphidromous fish also move between fresh and salt water, but not specifically to reproduce. Broad counts may include these fish because freshwater is part of their life cycle.
For that reason, the answer to “How many fish live only in freshwater?” is not the same as the broader global estimate of freshwater fish species. The counts above should not be read as totals for freshwater-only species.
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- Colorful Freshwater Aquarium Fish – Known for their spotted bodies, bright orange-red fins, and active swimming, Galaxy Rasboras bring a unique and eye-catching look to planted aquariums.
- Peaceful Community Fish – These small, calm fish are great for peaceful community tanks with other non-aggressive freshwater species of similar size.
- Perfect for Planted Tanks – Galaxy Rasboras look best in aquariums with live plants, driftwood, rocks, and open swimming areas where they can explore and display natural behavior.
- Carefully Packed for Live Delivery – Each order is prepared with care for safe live fish shipping. Slowly acclimate fish upon arrival before adding them to a fully cycled freshwater aquarium.
How much fish diversity is concentrated in freshwater?
Freshwater fish occur on every continent except Antarctica, from springs and headwater streams to large rivers, floodplains, lakes, and wetlands. Tropical regions are especially rich in species, with major concentrations in basins such as the Amazon, Congo, and Mekong.
The Food and Agriculture Organization of the United Nations (FAO) says freshwater ecosystems cover about 1 percent of Earth’s surface yet provide habitat for over 40 percent (13,000) of the world’s freshwater fish species. The FAO separately notes that another 2,000 fish species can also live in brackish water; that is a separate estimate, not an alternative count of strictly freshwater fish.
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- Pack of 6 Galaxy Rasboras – Add a beautiful group of Galaxy Rasboras, also known as Celestial Pearl Danios, to your freshwater aquarium for color, movement, and natural schooling behavior.
- Colorful Freshwater Aquarium Fish – Known for their spotted bodies, bright orange-red fins, and active swimming, Galaxy Rasboras bring a unique and eye-catching look to planted aquariums.
- Peaceful Community Fish – These small, calm fish are great for peaceful community tanks with other non-aggressive freshwater species of similar size.
- Perfect for Planted Tanks – Galaxy Rasboras look best in aquariums with live plants, driftwood, rocks, and open swimming areas where they can explore and display natural behavior.
- Carefully Packed for Live Delivery – Each order is prepared with care for safe live fish shipping. Slowly acclimate fish upon arrival before adding them to a fully cycled freshwater aquarium.
The IUCN/SSC Freshwater Fish Specialist Group says almost 90 percent of freshwater fish species belong to eight orders: carps, minnows and loaches; catfishes; characins and tetras; cichlids; toothcarps and killifishes; gobies; perch-like fishes; and bettas and gouramis.
Are freshwater fish species still being discovered?
Yes. Taxonomists continue to describe species and revise which scientific names are accepted. The 2025 CMS assessment reports 243 new freshwater fish species described in 2023 and 260 in 2024. Those are counts of new descriptions in those years, not numbers to add mechanically to any current catalogue total: catalogues may also revise or reclassify taxa.
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- Peaceful Community Aquarium Fish: Neon Tetras are calm schooling fish that do well in community freshwater tanks with other peaceful species of similar size and temperament
- Suitable for Planted Tanks: Their small size and vivid color make them a beautiful choice for planted aquariums, nano tanks, and natural-style freshwater aquascapes
- Approximate Size 1 to 2 cm: Each Neon Tetra is approximately 1 to 2 cm in length, providing active and colorful movement to enhance the visual appeal of your aquarium
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How many freshwater fish are threatened?
The IUCN/SSC Freshwater Fish Specialist Group’s overview says around one third of freshwater fish species are threatened with extinction and that 80 have been declared extinct. Its infographic reports 10,516 species assessed in the Red List categories shown. These figures describe the group’s assessment snapshot; they are not a comprehensive threat assessment of every species in the roughly 19,000-species global estimate.
The group identifies several pressures on freshwater fish:
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- Habitat loss and pollution
- Water over-abstraction
- Over-exploitation and illegal trade
- Invasive non-native species
- Loss of free-flowing rivers through hydropower and other infrastructure
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