Stunning New Amazon Killifish Found in Three Forest Pools May Already Be Endangered

In the Rio Cajari drainage of southern Amapá, in northern Brazil, a team of researchers working in small forest streams that locals call igarapés came across a fish that stopped them. It measured less than three centimeters in standard length. The males carried rows of bright orange spots along the front half of the body and bold orange chevrons near the tail, set against pale gray sides. The researchers have now described it as a new species, Laimosemion laranja.

The team was not looking for a showpiece. Lead researcher Yuri Abrantes, of the Universidade Federal do Rio Grande do Norte, said the group is developing a project on how life-history strategies evolved in freshwater fishes of the family Rivulidae across Brazil's different biomes. The scientists came from his university, the Instituto Peixe das Nuvens, the Universidade Federal do Pará and the University of West Florida. During sampling in the Rio Cajari region, Abrantes said, they found a fish with a coloration that immediately caught their attention. He described it as unexpected, unlike anything the team had seen in the study area, in both males and females.

Looks alone could not settle the question. The researchers examined body proportions, counted scales and studied features of the skeleton, then compared the results with closely related species. They also analyzed mitochondrial DNA. The genetic testing confirmed that the fish was a species not previously recognized. Abrantes said that at that point it became something special, an opportunity to add to knowledge of Amazonian biodiversity and to draw attention to areas that are poorly explored yet highly threatened.

The name carries two meanings. Laranja is Portuguese for orange, both the color and the fruit, and it also honors Laranjal do Jari, the municipality in Amapá where the fish was found. Abrantes said the team wanted a name that highlighted a trait of the fish while building a connection with the people of the region.

The species belongs to the killifish, a group of small freshwater fishes. Some killifish live in habitats that dry out periodically, and their embryos can halt development and stay dormant in damp mud until seasonal rains refill the pools. Abrantes noted that Laimosemion represents one of five independent origins of the annual life cycle within Rivulidae, and said L. laranja is of particular interest because it widens understanding of the group's diversity and evolution in the region.

The news about its prospects is less encouraging. Scientists have found the fish in only three small forest pools near Laranjal do Jari, and every known site shows signs of disturbance. One pool lies close to water discolored by sediment from mining. Another is inside the city itself, where plastic pollution is affecting the environment. Deforestation and urban development add pressure on the surrounding habitat.

The researchers estimate the species' entire known range at just 25 square kilometers. Given so small a range and multiple threats, they believe the fish meets the criteria for Endangered status under guidelines of the International Union for Conservation of Nature.

Their proposed remedy is specific: expand the boundaries of the nearby Rio Cajari Extractive Reserve so that it includes the pools where the fish lives. The study appears in the open access journal Zoosystematics and Evolution. Whether the reserve boundaries are changed will largely determine whether the species is studied further, or lost before it can be.