A team of scientists from Smithsonian’s National Museum of Natural History, the Federal University of Rondônia and the Federal University of Bahia has discovered two distinctive, undescribed species of the crenuchin genus Poecilocharax living in the tributaries of the Rio Aripuanã drainage, a large tributary of the Rio Madeira, Amazon Basin.
Poecilocharax callipterus. Image credit: Ohara et al., doi: 10.1093/zoolinnean/zlac026.
“It was exciting to find new species. But in the field, we saw the forest on fire, logging trucks carrying out huge trees, and cleared patches turned into cattle pasture,” said Dr. Murilo Pastana, a researcher with the Division of Fishes in the Department of Vertebrate Zoology at Smithsonian’s National Museum of Natural History.
“This made us feel a lot of urgency to document these species and publish this paper as quickly as possible.”
The two newly-described species belong to Crenuchinae, a subfamily of the fish family Crenuchidae distributed in the Amazon Basin with pronounced sexual dimorphism and exuberant color patterns.
“This small subfamily is highly desirable in the aquarium hobbyist market,” Dr. Pastana said.
“The exotic aquarium fish trade could pose yet another threat to the two new species even as scientists are first formally identifying them and learning of their existence.”
One of the new species, named Poecilocharax callipterus, has vivid red-orange fins and a distinctive dark spot just in front of its tail.
It inhabits the margins of what scientists call a black water stream, so named because its waters are stained the color of coffee by tannins leached from fallen leaves.
Males of the species have even more intense coloration and sport dorsal fins that can exceed half their body length, which averages just over an inch.
Poecilocharax rhizophilus. Image credit: Ohara et al., doi: 10.1093/zoolinnean/zlac026.
The second species, Poecilocharax rhizophilus, is an amber yellow with males possessing dark streaks in their dorsal and anal fins.
“But perhaps the most distinctive quality of this species is that it is so small that we consider it to be miniature, a designation given to any fish that is less than about an inch long when mature,” Dr. Pastana said.
“Lab study revealed that in these three-quarter-inch-long fish, parts of the skeleton that are typically bone are instead made of cartilage.”
The researchers encountered Poecilocharax rhizophilus among tangles of tree roots protruding from the banks of muddy watered streams.
Genetic investigations confirmed the evolutionary relationship of these two new closely related species and their relatives, bringing the total number of species in their small sub-family to five.
“These are the first representatives of Crenuchinae discovered after a gap of 57 years and the first records of Poecilocharax from the tributaries of the right bank of the Rio Amazonas draining the Brazilian crystalline shield,” the scientists said.
“These fishes are like works of art and losing either of these species would be like losing priceless masterpieces.”
The discovery is described in a paper in the Zoological Journal of the Linnean Society.
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Willian M. Ohara et al. The monophyly of Crenuchinae and description of two new species of Poecilocharax (Teleostei: Crenuchidae) based on phenotypic and genotypic evidence. Zoological Journal of the Linnean Society, published online May 16, 2022; doi: 10.1093/zoolinnean/zlac026
