Researchers have described a new species of brilliantly coloured fish from a network of forest streams in the Brazilian Amazon, and have already recommended it for listing as Endangered because of the pressures facing its only known home.
The fish, named Laimosemion laranja , is a killifish measuring less than three centimeters in standard length. Males are strikingly patterned, with rows of orange spots along the front half of the body and bold, chevron-shaped orange bars towards the tail, set against a pale grey flank.
It was found by Brazilian researchers from the Universidade Federal do Rio Grande do Norte , the Instituto Peixe das Nuvens, the Universidade Federal do Pará and University of West Florida , during fieldwork in the Rio Cajari drainage in the southern state of Amapá.
“We are developing a research project aimed at investigating the evolution of life-history strategies in freshwater fishes of the family Rivulidae across different biomes in Brazil,” said lead researcher Yuri Abrantes of the Universidade Federal do Rio Grande do Norte. “During our sampling in small rivers locally known as ‘igarapés’ in the Rio Cajari region, in Amapá State, we found this fish with a very striking coloration, which immediately caught our attention.”
Confirming that the fish was new to science required close comparison of its body proportions, scale counts and skeletal features against its closest relatives, together with an analysis of its mitochondrial DNA.
“It was an unexpected moment,” Abrantes recalled. “Initially, what most caught our attention was the impressive coloration of the males and females, which was unlike anything we had previously encountered in the study area. This sparked our admiration and a great deal of curiosity.”
Once the genetic analysis confirmed the fish's distinct identity, he said, “it was something special, as we saw an opportunity to contribute to increasing our knowledge of Amazonian biodiversity and to draw attention to the conservation of areas that are still poorly explored but highly threatened.”
The species' name, laranja , is Portuguese for both the colour orange and the fruit, a fitting nod to the males’ vivid markings. It also honors Laranjal do Jari, the Amapá municipality where the fish was found. “We wanted to choose a name that would highlight a characteristic of the fish while also fostering a sense of connection with the people of the region where it was discovered,” Abrantes explained.
Laimosemion laranja belongs to a group of Amazonian killifish, some of which have evolved an unusual survival strategy: their embryos can pause development entirely, lying dormant in damp mud until seasonal pools refill with rain. “ Laimosemion represents one of the five independent origins of the annual life cycle within the family Rivulidae,” said Abrantes. “ Laimosemion laranja is particularly interesting because it expands our knowledge of the diversity and evolution of this group in the region.”
The new species is currently known from just three small forest pools near Laranjal do Jari, all showing signs of disturbance from deforestation, mining and urban expansion; one site lies close to water discolored by mining sediment, while another, within the city itself, is affected by plastic pollution.
With its entire known range covering an estimated 25 square kilometers, the researchers argue that Laimosemion laranja meets the criteria for an Endangered listing under IUCN guidelines, and have recommended extending the boundaries of the neighboring Rio Cajari Extractive Reserve to help protect it.
The study is published in the open-access journal Zoosystematics and Evolution .
Zoosystematics and Evolution
A new killifish of the genus Laimosemion (Cyprinodontiformes, Rivulidae) from Rio Cajari in the Brazilian Amazon
20-Aug-2026