Two newly described Amazon fish species are on the brink of extinction

New varieties of South American darter fish were documented in Brazil’s Apuí region. But deforestation in the area means they may soon be extinct

Life 16 May 2022

The recently described Poecilocharax callipterus Average fish size ~3 centimeters

The recently described Poecilocharax callipterus species of darter fish is about 3 centimetres long

Murilo N.L. Pastana and Willian M. Ohara

Two newly described species of Amazon fish may already be headed for extinction.

When Murilo Pastana at the Smithsonian National Museum of Natural History in Washington DC set out with a group of colleagues to search for fish in less explored regions of the Amazon river basin, he didn’t know what they would find. A few days into their 2015 expedition, Pastana pulled a net from the water and was surprised to see small, vibrant orange fish in the plastic netting. The combination of long, reddish fins and a dark spot in front of the tail of the fish were unlike anything he had seen before.

“We knew right away that this fish was different,” says Pastana. “We were so excited, like little kids.”

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The 3-centimetre-long fish, now named Poecilocharax callipterus, was plucked from a stream in Brazil’s Apuí region. The researchers then combed the surrounding area to see if the fish lived elsewhere. That is when they found a second previously undescribed fish species among the tangled tree roots of a muddy stream bank. “I said, ‘Wait! There are two’,” says Pastana.

Unlike the orange fish they had found previously, this new specimen shared the subtle yellow-brown coloration of other fish species in the area. Once a lab analysis confirmed the new species, the team named the 2-centimetre-long fish Poecilocharax rhizophilus for its apparent love (“phil”) of roots (“rhiz”).

The recently described Poecilocharax rhizophilus , female specimen. Adults of this species are considered miniature fish since they are never longer than one inch. Fish size ~ 2 centimeters.

Poecilocharax rhizophilus individuals are just 2 centimetres long

Murilo N.L. Pastana and Willian M. Ohara

Genetic analyses have since verified that both fish are within the genus Poecilocharax, a subgroup of small freshwater fish known as South American darters. The species are the first additions to the genus since 1965.

In 2016, Pastana and his colleagues returned to carry out another extensive search, which confirmed what he had feared: P. callipterus, was limited to a single stream with roughly 4 square kilometres of habitat. P. rhizophilus was in a slightly less dire position, with a range of around 50 square kilometres.

In the six years since that exhibition, the forest home of the two fish species has been razed to make space for livestock, crops and gold mining – all of which decimate native flora and fauna.

Pastana thinks P. rhizophilus is probably still holding on, but he fears that even a small amount of human development could have destroyed the limited habitat of P. callipterus.

“Sometimes when we arrive in a region, it’s on fire because they have to clear the forest for livestock,” he says.

Pastana hopes this discovery spurs legal protections for the fish but admits it will be an uphill battle. He thinks the larger, brighter P. callipterus may find a home among aquarium hobbyists, which could at least sustain the species even if its native home is destroyed. “It’s not the best… but maybe it’s one way that this species will survive,” he says.

Journal reference: Zoological Journal of the Linnean Society, DOI: DOI: 10.1093/zoolinnean/zlac026

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