Envision a long, thin fish with a body that vaguely resembles an eel but is shorter, as if it lacked the rear end. Add two pairs of ventral fins, one dorsal fin and a delicate, transparent tail, such as the tails of aquarium fish. Now, reduce this image to fit in the palm of your hand.
The fish in question is approximately 10 cm long. It belongs to the genus Tarumania, and its appearance in no way resembles that of the piranha or tetra, relatives that live in South America’s rivers. It has been seen by only a handful of Brazilian ichthyologists (biologists who study fish). Tarumania walkerae is the only species in Tarumaniidae, a new family that has just been described.
New Amazonian fish species are described every month, sometimes twice or three times a month. A new genus crops up a few times a year. However, a description of a whole new family of fish is a surprise and is much rarer than these other discoveries.
Only five fish families have been discovered in the last 50 years. One is from South America (Scoloplacidae) and was described in 1976. Therefore, Tarumaniidae is the first description of a South American fish family in more than 40 years.
“Why has it taken so long to be discovered? Biologists have been collecting in the region for ages,” said ichthyologist Mario Cesar Cardoso de Pinna, Full Professor at the University of São Paulo’s Zoology Museum in Brazil. English naturalist Alfred Russel Wallace (1823-1913) collected fish specimens from the Negro in 1850-52.
De Pinna explained that T. walkerae lives deeply buried in leaf-litter deposits that accumulate and rot at the bottom of pools or rivers, sometimes several meters below the surface.
“It’s always in hiding,” he said. “The species has never been collected with a net for the obvious reason that it doesn’t inhabit open water but [rather] spends its entire life submerged in pools full of leaf deposits one or two meters below the surface, and during the rainy season, it can be covered by six to seven meters of water column.”
“These pools, which are often very deep, lie along the Tarumã-Mirim, an intermittent stream that when it isn’t dry, flows into the Tarumã River, a left-bank affluent of the Negro not many kilometers from Manaus.”
De Pinna and colleagues Jansen Zuanon and Lucia Py-Daniel at the National Institute for Research on Amazonia (INPA) are the authors of the study describing the new family Tarumaniidae, which belongs to the order Characiformes, with more than 2,000 species in South America and Africa, including the piranha, piraba, pacu, tetra and wolf fish.
The study, which was published in Zoological Journal of the Linnean Society, was supported by FAPESP.
The first Tarumania specimen, a young individual, was collected in 1999 from the Tarumã-Mirim by Swiss biologist Ilse Walker, a researcher at INPA since 1976. Walker donated the specimen to INPA’s fish collection in 1999.
She could not recall the exact conditions in which she had collected the little fish. The specimen was evidently different from everything known to INPA’s ichthyologists, but elements were lacking to describe the species. An adult specimen would be needed for this purpose.
The mystery about where other fish of the same species could be found lasted until 2006, when its hiding-place was finally discovered. Zuanon collected an adult specimen in a leaf pool near the Tarumã-Mirim. It was the dry season in the Amazon, and the pool was in the middle of the forest several hundred meters from the stream. The area is flooded during the wet season.
“Tarumania is a rare and highly intriguing discovery,” De Pinna said. “It’s an extraordinary genus in many respects. The environment it inhabits is unusual, for example.”
The fish lives in an interstitial water environment covered by meters of leaves and other detritus. During the wet season, this watery carpet is several meters deep. In the dry season, most of the water is absorbed by the subsoil or evaporates, leaving pools only a couple of meters deep in which the fish lives.
Several other specimens were collected in 2010 and 2016. Why did it take so long to describe the new species and the new family Tarumaniidae? “To propose a new family, you must demonstrate that it’s phylogenetically equivalent to other groups of fish,” De Pinna said.
A new phylogeny (Characiformes) was required, he explained. This process was a laborious, time-consuming task as it entailed studying dozens of species all over again to compare their morphology with that of Tarumaniidae. This method was the only way to identify similarities with other Characiformes and distinguish unique traits that justify the naming of a new family. “We found the place of Tarumania in the ‘Tree of Life’. It’s clearly close to the wolf fish, Hoplias malabaricus,” he said.
The description, which has now been published, was based on morphological phylogeny. A second study, detailing the group’s molecular biology, is in progress. “The preliminary results confirm that it is indeed a new family,” De Pinna said.
Now that T. walkerae is known to inhabit leaf-litter pools near the Tarumã, this environment will be visited by ichthyologists to collect Amazonian specimens. After all, such pools are by no means exclusive to the Tarumã; rather, they are found throughout the Amazon region.
“It’s practically certain that Tarumaniidae will grow as a family. The discovery of such a distinctive species in a relatively accessible location shows how much we still have to learn about fish diversity in Brazil,” De Pinna said.
Source : By Peter Moon | Agência FAPESP