From deep dark Meghalaya cave, explorers bring to light ‘world’s largest’ subterranean fish
Written byTora Agarwala
| Guwahati |Updated: February 13, 2020 9:24:13 pm
When in February 2019, Daniel Harries, a biologist from the Heriot-Watt University in Scotland, came across the fish, the first thought that crossed his mind was: “I am going to need a bigger net!”
In a cave in a remote forested area of Meghalaya’s Jaintia Hills, Harries, part of an annual expedition called ‘Caving in the Abode of Clouds’, remembers being surprised by how large the fish was after he pulled it out of the pool. “It was just over 40 cm! The hand net I had was around 10 cm X 15 cm — which made me feel rather foolish,” he says, in an email.
But it would be unfair to fault Harries for carrying a net of that small a size. The 250-known subterranean (occurring under the earth’s surface) fish species around the world measure only around 8.5 cm on average.
A paper published in November 2019 in the journal Cave and Karst Science describes Harries’s accidental discovery as “world’s largest known subterranean fish.” While initial investigations have begun, only further morphological and genetic studies will give clarity on this rare distinction of being the world’s largest. The fish is yet to be named.
“It is nearly five times the mean length (85mm/8.5 cm) for all known subterranean fish to date. The only other species exceeding 300mm (30 cm) in length are eel-like Synbranchidae with nothing like the bulk of the new fish,” states the paper co-authored by Harries, professional cave explorer Thomas Arbenz, Neelesh Dahanukar of the Institute of Science Education and Research, Pune and Rajeev Raghavan of the Kerala University of Fisheries and Ocean Studies, Kochi.The 250-known subterranean (occurring under the earth’s surface) fish species around the world measure only around 8.5 cm on average. (Photo courtesy: Daniel Harries)
Dahanukar and Raghavan are involved in identifying, classifying and naming this fish. “We will be carrying out detailed studies on the morphology and genetics of the fish and comparing it with other species in the same genus/family and arriving at a conclusion,” wrote Raghavan in an email.
According to Raghavan, who is also the South Asia Coordinator of the IUCN Freshwater Fish Specialist Group, “Subterranean ecosystems are considered extreme, high-stress environments characterised by darkness, truncated food webs and food scarcity. Despite this, they harbour exceptional vertebrate and invertebrate taxa (21,000+ species), many of which are evolutionarily unique, and relics of ancient fauna given their long-term isolation.”
He adds that: “Many cave fish show different adaptations – some don’t have eyes, some have reduced eyes, some don’t have fins, some have weird body shapes. All of this depends on the species/groups.” The new discovery, too, does not have eyes.
The experts feel that the fish species is very similar to the Golden Mahseer or the Tor Putitora, one of the most famous game fish of the Himalayan rivers. “Unique characters that distinguishes it from the Golden Mahseer is the lack of pigmentation, a lack of eyes and of course, its subterranean habitat – being locked in caves!” says Raghavan. Adds Harries: “We think there are ‘normal’ Golden Mahseer in the area too but there is not much surface water (at least in the dry winter months) so fish end up in the cave pools and underground rivers.”
“The specialists say that possibly one (or more) populations of these fish became isolated deeper in the caves and over generations became adapted to the dark, losing their eyes in the process,” explains Harries.
So what does this fish feed on? “No clue at all,” says Raghavan, “But there might be lots of aquatic invertebrates in the water and even smaller fish.”
The fish was apparently first seen in 1998, say the explorers. However, due to lack of documentary evidence, it is not possible to verify the same.
Started in 1992, as an annual caving expedition by explorers from around the world, ‘Caving in the Abode of Clouds’ project has recorded a number of cave species in the past including two bats (Murina jaintiana and Murina pluvialis), a spider (Heteropoda fischeri), a fish (Schistura papulufera).
According to Harries, this discovery brings to light the importance of cave conservation in Meghalaya. In the state’s unique topography, there is a network of more than 1500 identified caves — and many more unexplored till date.
“Systematic exploration of the Meghalayan caves has been underway for almost 30 years and hundreds of kilometres of cave passages have been explored and mapped. Nevertheless, this very large cave fish remained undocumented until last year. This raises questions about what else might have been overlooked in the caves,” he says.
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