309 new species of freshwater fish from around the world were described in 2025, making it a “bumper year” for freshwater discoveries.
Among the new finds on the annual New Species report, a collaboration between freshwater conservation charity Shoal, the California Academy of Sciences and global taxonomists and institutions, is the sicklefin redhorse (Moxostoma ugidatli), which lives in the Tennessee River basin, stretching across North Carolina and Georgia in the United States. The researchers described the fish as “perhaps the largest truly new North American species discovered in the past half century.” Its name ugidatli derives from the Cherokee language, meaning ‘wearing a feather’, a nod to the fish’s most distinctive feature: a tall, sickle-shaped dorsal fin.
Scientists also described the black arrow tetra (npaichthys luizae), which is notable for its gold with black oblique stripes. Found in the Rio Tapajós basin of Brazil, the fish is considered so beautiful that individuals were being sold for more than $100 (£75) each, before its description qualified it for conservation protection.
Others new additions range from cave-dwelling fishes in China – including the Yang's plateau loach – to minnows in Anatolian streams, as well as the ancestor cory (Hoplisoma noxium), found in the Amazon basin in Pará state, Brazil, which is known to produce powerful toxins when stressed that can kill other fish when kept in close proximity after capture.
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“309 new freshwater fish species in a single year is the third highest amount described since records began in 1758,” says Mike Baltzer, executive director of Shoal. “The average this century has been around 250, so 2025 was a bumper year.
"Partly, it reflects improved scientific capacity. Taxonomists are working with better tools and there is growing local expertise in biodiversity hotspots. Previously remote habitats are becoming more accessible, although the same forces that allow us to discover new species can be the forces that threaten them.
"What this figure ultimately tells us is that freshwater biodiversity is far richer than we’ve documented. There’s an extraordinary amount of life yet to be described. But until species are formally recognised and named, they’re effectively ‘invisible’ to conservation. Discovery is the first step towards protection.”
Freshwater ecosystems cover less than 1% of the Earth’s surface. The New Species 2025 report showcases species from rivers, lakes and wetlands that have only just been recognised by science. Each one represents years of fieldwork, taxonomic expertise and international collaboration. Many are likely to be found nowhere else on Earth.
Four African annual killifishes in the Nothobranchius genus are also described: the rainbow killi, marbled killi, Katemo Manda’s killi and the Dubie Killi. “Like all annual killifish, they have one of the most remarkable life cycles in the vertebrate world,” Baltzer explains. “They live in temporary pools that form during the rainy season, sometimes no larger than a puddle. The adults hatch, grow, mature and reproduce in a matter of weeks. Before the pools evaporate, they lay eggs. When the dry season comes, the adults die and the habitat turns to dust. But the eggs remain, lying dormant in bone-dry earth for months, sometimes longer, waiting for rain. When the rains return, the next generation hatches and the cycle begins again. It’s a life lived against the clock – an evolutionary response to extreme seasonality. These fishes are small, often jewel-bright, and astonishingly resilient. They remind us that even the tiniest, most ephemeral habitats can harbour extraordinary evolutionary stories.”
Freshwater fishes are among the most threatened vertebrates on the planet. According to the IUCN, around one in three assessed freshwater fish species are threatened with extinction. Habitat loss, dams, pollution, invasive species and climate change are driving declines that often go unnoticed compared with terrestrial wildlife crises, despite the fact that freshwater ecosystems support food security, drinking water, cultural heritage and the livelihoods for billions of people.
Of all the world’s freshwater fish species described last year, only one has so far been assessed for the IUCN’s Red List of Threatened Species: Nothobranchius sylvaticus, a forest killifish from Tanzania, which researchers listed as Critically Endangered.
Other species profiled are already thought to be highly threatened, and would likely be listed as Critically Endangered on assessment. Newly found species can wait years for formal conservation assessment. But without Red List assessments, conservationists lack the data needed to prioritise action, secure funding and protect habitats.
By spotlighting newly described freshwater fishes, Shoal hopes to raise awareness and increase support for conservation. “On one hand, there is real cause for celebration,” says Baltzer. “The fact that we’re still describing hundreds of freshwater fish species each year speaks to the extraordinary richness of life in freshwater, and to the dedication of researchers around the world who are uncovering it. There is something profoundly hopeful in knowing that our planet still holds so many biological secrets.
"But there is also a sobering reality. Many of the newly described species are rare, range-restricted, and already under pressure. Some inhabit single river systems or isolated wetlands that are being altered faster than we can document them. We are almost certainly losing species before we even know they exist.
"Every species described represents not just a fish, but an entire ecological story, a web of interactions, evolutionary history, and habitat specificity. Discovery must go hand in hand with protection.”
New Species 2025 is available to download.
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