“Lost Beauty”: Fish thought extinct rediscovered after 20 years

When researchers examined an inconspicuous, shallow pond on the edge of a remote remnant forest in Bolivia in spring 2024, they had no idea that right there—beneath leaves, gray mud and surrounded by vast agricultural land—they would find a species many already believed to be extinct: Moema claudiae, a seasonal killifish that had been considered lost for more than 20 years.

The scientific details of the rediscovery were published by Heinz Arno Drawert and Thomas Otto Litz in the journal Nature Conservation. Their study shows: This rare species has survived—and is now getting a surprising second chance.

A fish that survives in the soil

Moema claudiae belongs to the South American egg-laying killifishes—better known as killifish or seasonal fishes—in the family Rivulidae. These fishes have one of the most extraordinary reproductive strategies in the animal kingdom: they live in temporary waters such as puddles, ponds or seasonally flooded forest depressions that dry out completely during the dry season. While the adult fish then die, their eggs survive in the muddy soil. In a special resting phase (diapause), they can withstand months of drought. As soon as the rainy season begins, life in the substrate awakens—the eggs hatch, and a new generation begins its annual cycle.

However, their extreme specialization also makes seasonal fishes especially sensitive to human disturbance. If such a temporary water body disappears or no longer fills reliably, the entire population is usually lost as well.

From first discovery to the status “Possibly extinct”

Moema claudiae was first described in 2003 by the Brazilian ichthyologist Wilson J. E. M. Costa. The type specimens came from a temporary wetland in the floodplains of the Río San Pablo in the Bolivian lowlands—a landscape that at the time still consisted of a mosaic of forest, savanna and seasonal ponds.

As in many parts of the Amazon region, this area changed rapidly. The original site was completely destroyed: a settlement was built, forests were cleared, and the surroundings were converted on a large scale into agricultural land. Pesticides, fertilizers and altered water regimes placed additional stress on the ecosystem. The small ponds on which M. claudiae depends were drained, filled in or contaminated. The once dense vegetation disappeared within a radius of several kilometers.

Several intensive search campaigns in the area around the original site were unsuccessful. Since the species was known only from this one locality and no record had been obtained for more than two decades, the IUCN eventually classified Moema claudiae as “critically endangered, possibly extinct.”

Bolivia is among the countries with the highest recent losses of tropical primary forest—and it is a global hotspot for killifishes: 32 species are known there, 19 of them endemic and nine documented exclusively from their type localities.

Still there after all: A pond in the remnant forest

In April 2024, Drawert and Litz again surveyed the remaining forest fragments and seasonal waters of the region. One of their goals was to either rediscover Moema claudiae or confirm the species’ final loss. They succeeded.

The site was a small blackwater pond in a seasonally flooded strip of forest, no more than 40 centimeters deep, a narrow relic framed by vast agricultural fields. The substrate consisted of a thick layer of leaf litter over gray clay, with no submerged plants and only a little grass along the shore. This new site lies about 100 kilometers northwest of the place where the species was discovered in 2003—and is likewise already threatened by agricultural use.

In this pond, the researchers caught several small, brightly colored killifish. By the time they reached the lab, it was clear: these were unmistakably Moema claudiae. For the first time, living individuals could be photographed and their behavior documented. Particularly striking is the males’ large, black, vertically oriented shoulder spot—an important feature that distinguishes the species from closely related ones.

This confirms that Moema claudiae is not extinct, but survived in a tiny remnant habitat right at the edge of the fields.

A hotspot: 6 more killifish species

Surprisingly, in the same pond the researchers found six other species of seasonal killifish alongside M. claudiae—more than had ever before been documented in a single water body. The accompanying species included Pterolebias longipinnis, Moema beucheyi, Spectrolebias filamentosus and Papiliolebias habluetzeli.

Normally, only a few highly specialized seasonal fish species coexist in the same habitat because they occupy very narrow ecological niches. But here several ecological zones meet: the Amazon rainforest, the savannas of the Llanos de Moxos and the catchments of two major river systems. This interaction creates an exceptionally diverse mosaic of microhabitats—and makes the small pond a hotspot of global importance.

The habitat of M. claudiae is disappearing

In their study, Drawert and Litz also show how dramatically the region has changed over recent decades. Between 2001 and 2024, Bolivia lost almost ten million hectares of forest—more than half of it primary, humid tropical forest. In 2024 alone, more than 1.8 million hectares of tree cover disappeared. Especially affected are the lowland areas in northern Santa Cruz and southern Beni Department—precisely the regions where Moema claudiae occurs.

The main drivers of this development are:

• the expansion of the agricultural frontier,
• large-scale soy and other monocultures,
• slash-and-burn clearing,
• as well as new roads and settlements.

For species such as M. claudiae, which depend entirely on small seasonal ponds, this development means a gradual loss of their entire basis for survival.

There is also another factor: Deforestation is significantly altering rainfall patterns in the Amazon region. A study published in Nature in March 2025 shows that heavy rainfall occurs more often over cleared land during the rainy season, while the dry season becomes even drier in many places. For killifish, this is fatal: heavy rain can wash out the eggs, while extreme dry periods cause them to die in the soil. Together with ongoing deforestation, this creates a dangerous mix of habitat loss and climatic destabilization that greatly hinders the survival of highly specialized species such as M. claudiae.

Act now—before the species disappears again

The scientists stress the urgency: the rediscovered pond is currently the only known habitat of Moema claudiae. Without consistent conservation measures, even this last population could be lost quickly.

They therefore recommend:

• immediate protection of the discovery site, ideally by designating a small legally protected area,
• systematic mapping of additional seasonal ponds in the region in order to track down possible further populations,
• close cooperation with communities and landowners to minimize conflicts over land use,
• the development of long-term management plans that better reconcile agricultural use and biodiversity.

As an additional safety measure, they suggest examining whether a conservation breeding program under controlled conditions could be established—for example together with local research institutions or international experts on seasonal killifish.

But one thing is just as clear: even the best breeding station and the most careful monitoring cannot stop the underlying threat. In the end, what matters is slowing the ongoing deforestation and preserving the remaining habitats—before Moema claudiae disappears a second time.

Not everything is lost yet

The story of Moema claudiae shows that even tiny, inconspicuous species can have enormous significance. It reminds us that some species are considered extinct only because we can no longer find them—not because they have truly vanished. And it highlights how many more species disappear unnoticed long before they are even discovered or scientifically described.

For M. claudiae, it is not too late. But the rediscovery of this species also makes clear that in conservation we must not rely on lucky coincidences. Habitats must be protected proactively, before species are pushed to the brink of disappearance, not only afterward.

The return of this small killifish is a glimmer of hope and proof of how remarkably resilient nature can be when it is left even the smallest refuges. At the same time, it is a warning to act quickly: while species such as the Ash Meadows killifish are already irretrievably lost, Moema claudiae shows what can still remain possible—if we act in time.

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Source

• Drawert, H. A., & Litz, T. O. (2025). Rediscovery of a thought to be extinct beauty: A second chance for conservation. Nature Conservation, 60, 115-124. https://doi.org/10.3897/natureconservation.60.160386