Enigmatic aquifer fish discovered in India

Computer-generated tomography image of the skull of Horaglanis populi in frontal view. Photo: Britz/Senckenberg

A citizen science project in India, tasked with finding out more about the lives of tiny catfish that inhabit underground aquifers, has revealed a whole new species.

Life in aquifers - underground rock layers that transmit water to wells and springs - is characterised by complete darkness and low concentrations of nutrients, carbon and dissolved oxygen. It sounds pretty uninviting, and of nearly 300 species of fish that live in subterranean aquatic habitats, only 10% of them are found in aquifers.

Some of these fish are now under threat of extinction, and as part of a citizen science project, an Indian-German team of researchers has undertaken a study of the catfish genus Horaglanis, found in the aquifer in the state of Kerala. The tiny members of this genus, which are only about 30mm long, are blind and lack any pigment as they live without light.

“There are very few documented occurrences of these species – as a rule, these elusive little fish only come to the surface when a domestic well is being dug or cleaned,” explains Dr Ralf Britz of the Senckenberg Natural History Collections in Dresden, Germany.

“Local people are often the only ones who get to see such well-hidden species. Therefore, they can play an important role in improving our scientific knowledge of this unusual fauna."

Ralf Britz, Senckenberg Natural History Collections

For this reason, Britz and his colleagues from the University of Kochi, led by Dr. Rajeev Raghavan, and Dr Neelesh Dahanukar from Shiv Nadar University in Delhi, also relied on the cooperation of local citizen scientists. Over a six-year period, they conducted a series of workshops, focus groups, and informal conversations with communities at several sites.

“Local people are often the only ones who get to see such well-hidden species," said Britz. "Therefore, they can play an important role in improving our scientific knowledge of this unusual fauna.

"We informed local villagers about the importance of subterranean fish species and their conservation needs and asked them to share information, photos or videos with us when they encountered or collected these species.”

The researchers complemented this citizen science approach with targeted collection efforts in wells and above-ground storage tanks, with scoop nets in shallow wetlands, water channels, home gardens, and plantations, and with the use of baited traps in excavated wells on farmsteads, in ponds, and caves.

The newly discovered subterranean fish species Horaglanis populi. Image: CP Arjun

Britz explained, “This allowed us to generate datasets with a total of 47 new site detections and 65 new genetic sequences. These show, among other things, that Horaglanis are endemic to the part of Kerala state south of the Palghat Gap – the mountain pass apparently represents a biogeographical barrier for the subterranean world as well.

“The genus is characterised by a high level of genetic diversity that has evolved over millions of years – although the fishes’ appearance has changed remarkably little.”

As well as gathering information on existing species of the aquifer dwelling catfishes, the team succeeded in identifying a new one. Horaglanis populi measures no more than 32 millimeters, has no eyes and a blood-red body. It is genetically distinct from the three previously known Horaglanis species.

“The specific name populi, the genitive of the Latin noun for people, honours the invaluable contributions of the interested public in Kerala who helped document the biodiversity of these subterranean fishes – including the discovery of the new species,” says Britz. “Our Horaglanis project is an excellent example of how public involvement can greatly increase our knowledge of rarely collected organisms that live in relatively inaccessible habitats.

"Local people expand the researchers’ eyes and ears by several orders of magnitude.”

Villagers played an important role in identifying the aquifer catfish species in their well water. Image: CP Arjun

Species with small ranges – such as Horaglanis populi – are considered to be at high risk of extinction, especially if they live in subterranean habitats. According to the study, fishes in the study area enjoy little or no protection under local or regional laws, and their habitats are embedded in densely populated landscapes.

Both groundwater extraction and mining of laterite rock layers threaten the animals.

“To ensure the survival of Kerala’s enigmatic subterranean catfishes, a planning and implementation approach involving a wide range of stakeholders is needed. This must also include the local population, whose support was instrumental in advancing our research to its current state,” concludes Britz.

The researchers were able to gather information on the distribution of the animals, their genetics, and evolutionary history – and they discovered a new species based on genetic studies. The study was published in the the journal Vertebrate Zoology.