Guwahati: The largest known cavefish from Meghalaya has been named after the state’s indigenous Pnar community.
Roughly three years back, an international team of cave explorers from India and other countries encountered a new cavefish in Jaintia Hills of Meghalaya and a return visit was made in January to gather more information on the fish.
But they could not ascertain the fish species. Dan Harries of Grampian Speleological Group was one of the members of the expedition.
After a detailed analyses and molecular analyses, scientists have found that the world’s largest cave fish from Meghalaya, is actually a new species, Neolissochilus pnar.
A paper published in the Vertebrate Zoology journal reveals details of the new species. The paper has been authored by Neelesh Dahanukar of Department of Life Sciences, School of Natural Sciences, Shiv Nadar Institution of Eminence; Remya L. Sundar of Department of Fisheries Resource Management, Kerala University of Fisheries and Ocean Studies; Duwaki Rangad of Department of Zoology, St. Edmund’s College, Laitumkhrah, Shillong; Graham Proudlove of Department of Entomology, The Manchester Museum, University of Manchester and Rajeev Raghavan of Department of Fisheries Resource Management, Kerala University of Fisheries and Ocean Studies.
The world’s largest subterranean fish was discovered in 2019 and was tentatively identified as a troglomorphic form of the golden mahseer, Tor putitora. Detailed analyses of its morphometric and meristic data, and results from molecular analyses now reveal that it is a new species of the genus Neolissochilus, the sister taxon of Tor.
Subterranean fish typically lack pigmentation and are white or pinkish in colour. Their eyes are reduced in size or entirely absent.
“The unique characters that diagnose N. pnar from all others comprise highly reduced eye size to complete absence of externally visible eyes and complete lack of pigmentation,” the study says.
The authors in the paper say they have formally described the new species as Neolissochilus pnar, honouring the tribal communities of East Jaintia Hills in Meghalaya, from where it was discovered. ‘Pnar’, is the sub-tribal group of the Khasi people in Meghalaya.
The limestone caves of Meghalaya harbour a remarkable diversity of subterranean taxa and the state is one of the two hotspots of subterranean fish diversity, the other being the laterific acquifers of Kerala.
Roughly 1.6% (293 species) of all known (~18,000) freshwater fish species live their whole lives either in caves or in groundwater aquifers. These ‘troglobiotic’ or ‘stygobiotic’ fishes occur in 36 countries across six continents, with China harbouring close to one-third (96 species) of the global diversity, followed by Brazil (43 species), Mexico and India (18 species each).
The specimens of study were collected from the Krem Um Ladaw and the Krem Chympe caves in Jaintia Hills, Meghalaya in 2019 and 2020.
The entrance to the cave in Krem Um Ladaw is in the form of a large open pitch head, lies in a large, rocky, seasonally dry streambed within a forest. The entrance series is predominantly vertical with some short(<20 m) horizontal to steeply sloping sections. After descending for just over 100 m, the entrance series drops into a horizontal and relatively narrow (3–4 m) streamway, the floor of which has several pools of standing water. The cave floor is predominantly rocky with areas of bedrock, boulders and coarse gravel. The floor of the boulder passage is mostly elevated well above water level although there are pools in places along the left wall.
The fish reside in small-sized (~3m x 4m) to large (>10m x 10m) pools. Although the invertebrate community in the cave is plentiful, it is not noticeably more abundant than that of many caves in Meghalaya.
Amongst the terrestrial invertebrates were brown crickets, cellar spiders and fungus gnatlarvae. No significant bat roosts were encountered, and therefore no guano deposits or other obvious sources of nutrients were observed within the cave.
Unlike Um Ladaw, the Krem Chymphe, where one of the paratypes was collected, is a broadly horizontal river cave, with a massive tunnel of deep water, and various small waterfalls/ dams inside. Neolissochilus pnar occurs here in pools in a side passage.
“It is conceivable that seasonal flood debris (bamboo, tree branches and leaf litter) carried into the cave from the surrounding forest provides the primary food source for the fish population. There is no plant growth in the caves and in the absence of bat guano, there is probably no other primary energy source in the habitat,” the study says.
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“Despite the ichthyofaunal richness in aquifers and caves on the Indian subcontinent, there is only a limited number of studies dealing with their diversity and distribution. Recent descriptions of not only new species but also new genera and even family level taxa of freshwater fishes from the subterranean waters of India suggests major knowledge gaps in our understanding of these largely inaccessible habitats of the Indian subcontinent. Given that these habitats are also the most vulnerable to a number of anthropogenic activities, there is an immediate need to explore and understand the hidden diversity of subterranean realms in the region,” the study says.
The study says the description of the world’s largest subterranean fish Neolissochilus pnar is, therefore, likely to drive further explorations and understanding of this unique habitat and its remarkable fauna.
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