The newly-discovered species belongs to Horaglanis, a genus of rarely-collected, tiny, blind, pigment less, and strictly aquifer-residing catfish.
Horaglanis populi. Image credit: C.P. Arjun.
Horaglanis is a genus of catfishes, remarkable for their bizarre appearance (blind, pigmentless and of blood-red coloration), tiny size (less than 3.5 cm), occurrence in a unique habitat (lateritic aquifers), rarity (appearing only occasionally in dug-out wells), paucity of museum specimens.
It currently includes four species endemic to the southern Indian state of Kerala.
“The lateritic aquifers of Kerala harbor a unique assemblage of enigmatic stygobitic fishes which are encountered very rarely, only when they surface during the digging and cleaning of homestead wells,” said Dr. Ralf Britz from the Senckenberg Natural History Collections and colleagues.
“We focused on one of the most unusual members of this group, the catfish Horaglanis.”
“There are very few documented occurrences of Horaglanis species — as a rule, these elusive little fish only come to the surface when a domestic well is being dug or cleaned,” Dr. Britz said.
“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.”
“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 and/or collected these species.”
“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.”
Named Horaglanis populi, the new species occurs in the lateritic aquifer systems in the Alappuzha and Pathanamthitta districts of Kerala, southern India.
The specimens were collected from dug-out wells in the towns of Malapally, Edanadu, and Chengannur, and the nearby village of Thiruvanvandoor.
Horaglanis populi has a blood-red body, four pairs of well-developed barbels, and measures less than 3.2 cm in length.
The fish is blind and pigmentless, and is genetically distinct from the three previously known Horaglanis species.
“Species with small ranges, such as Horaglanis populi, are considered to be at high risk of extinction, especially if they live in subterranean habitats,” the authors said.
“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.”
The discovery of Horaglanis populi is reported in a paper in the journal Vertebrate Zoology.
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R. Raghavan et al. 2023. Evolution in the dark: Unexpected genetic diversity and morphological stasis in the blind, aquifer-dwelling catfish Horaglanis. Vertebrate Zoology 73: 57-74; doi: 10.3897/vz.73.e98367
