A decade ago, Wimarithy K. Marak, a resident of Assam’s Goalpara district, often used to encounter a small pink creature in her neighbourhood’s wells. She simply thought of it as a worm infesting her locality. In 2021, after she became a researcher, she stumbled upon the creature again while drawing water from a well. “This time I sent the picture to my supervisor and we brought a specimen to the lab,” she says.
The creature turned out to be a two-centimetre long blind loach with a body so transparent that its blood and internal organs give it a striking blood-red appearance. The first specimen was collected in March 2021. Although further explorations into neighbouring wells yielded no results for the now described Gitchak nakana, the team of researchers had requested village residents to alert Marak if they came across anything unusual in their wells.
Much later in 2024, when one of Marak’s relatives was cleaning his well, he came across what seemed like a worm. “My relatives had fully drained the well and that is when they found a specimen of another subterranean species,” she says. Named Rakthamichthys anchi, the holotype, measuring around 310 mm, was collected in May 2024. R. anchi is a slender eel-like fish which shares characteristics with Gitchak nakana.
Researchers then published two papers earlier this year describing both the species. Kangjam Velentia, a co-author of both the studies, says that the wells from which the specimens have been collected are kept very clean and often used for drinking purposes. “We intentionally did not reveal the exact locality where the fishes have been found, since we were afraid that the populations might be exploited,” she adds. On Rakthamichthys anchi, Velentina shares that the species belongs to the fish family Synbranchidae – also commonly known as the swamp eel family.
According to the study on R. anchi, it is a new species of phreatobitic synbranchid eel from Assam. A phreatobiotic organism refers to one which lives in a subterranean groundwater environment, particularly water filled species within an aquifer.
Testing for evidence
Synbranchids are highly elongated, eel-like percomorph fishes, with around 28 valid species, distributed across Central and South America, West Africa, large parts of Asia and Australia. “We are sure that they (R. anchi) are groundwater species and they travel through those aquifer layers,” says Velentina.
After the collection process, specimens were photographed and preserved for forensic examination. The Indian team collaborated with researchers in Germany where micro CT scanning was performed. According to Ralf Britz, a German ichthyologist who is also the lead author of both the studies, the area in which both G. nakana and R. anchi have been found is the most unexpected habitat for subterranean fishes. “The wells are situated in alluvial deposits, a quickly changing environment, in which it is difficult to imagine how a subterranean fauna evolved,” he says. Britz was involved in the micro CT scan of these organisms.
Risks of human-fish conflict without awareness
Talking about how people often confuse such fishes with earthworms or even juvenile snakes, Rajeev Raghavan, a professor at the Kerala University of Fisheries and Ocean Studies (KUFOS) in Kochi, says most people have a typical idea of what a fish looks like. “This can lead to human-fish conflicts as people may think fishes like R. anchi are toxic and their first reaction is often to kill them,” says Raghavan who is also a co-author on the Gitchak nakana study.
Raghavan and his team have been working with local communities in Kerala to raise awareness about such fishes. He says that wells provide an opportunity to peek into this subterranean habitat which is otherwise inaccessible. However, he cautions, “We are sure that R. anchi and G. nakana live in aquifers and not just the wells alone but we do not know why they venture into these semi-open systems.” Aquifers are extreme ecosystems with no light, limited oxygen and a dearth of available food, he explains. “Perhaps wells with their greater food availability, in terms of fallen particles, insects and leaves as well as more light and oxygen attract them for feeding opportunities,” Raghavan adds. “What makes such fishes so peculiar is their low metabolic rate. Once they feed, they can go for months without food.”
The well from which G. nanak specimens were collected is around 6.7 metres deep and 1.5 metre in diameter. The area is dominated by alluvial deposits, which the Geological Survey of India describes as highly oxidised dark brown to reddish brown loamy sand. R. anchi too was found in similar conditions.
The groundwater in the Brahmaputra basin flows from elevated southern highlands towards the northern plains with the river itself acting as a major hydrological boundary. As Prerona Das, a geologist at North-Eastern Hill University puts it, “Sometimes even earthquakes can induce connectivity between the river and surrounding aquifer system.
“The Brahmaputra floodplain hosts five to six multi-layered aquifers extending to 400 metres depth consisting of medium to coarse gained sand depicting high lateral connectivity resulting in high yield aquifers,” she says. According to Das, the entire aquifer system is capped with a clay layer with variable thickness from five metres to 60 m.
Alluvial aquifers
Alluvial aquifers occur where there are saturated (water-filled) sediments below ground with the environment being totally dark, explains professor Grant Hose, an aquatic ecologist and ecotoxicologist from the University of Sydney’s School of Life and Environmental Sciences. Hose is not associated with the two studies. According to him, oxygen and nutrients that reach aquifers come either from the surface seeping through the soil or from rivers or wetlands which are connected to the aquifer.
“The sediments that make up the aquifer provide small spaces between the grains where small animals are able to live,” he says. “The spaces between such grains impact how big the animals living in the aquifer can be. Hence, It is rare to find stygofauna living in aquifers with clay,” he adds. Stygofauna are defined as animals that live in groundwater, especially in underground water-filled spaces.
Grant shares that stygofauna are important for aquifers and groundwater ecosystems since they graze on bacteria and prevent clogging. “When stygofauna graze on bacteria they cycle the carbon and make it available again for other organisms,” he adds. However, the diet of G. nakana and R. anchi needs to be studied.
However, Grant also cautions that wells can sometimes give a misleading picture of what actually lives in the aquifer. “Wells can act as a trap as it is an open body of water which I think is easier for animals to move through than an aquifer’s sediments,” he says. To make sure a fish is actually present in an aquifer, he suggests sampling the well for eDNA after it is purged of its water.
“All animals leave behind their DNA when they move through an environment. By analysing the groundwater for fish DNA we could determine if the fish was present in that area without having to actually catch it,” he says.
The need to monitor and map habitats
Any sort of impact observed on surface water actually percolates into the groundwater, Raghavan explains. “If we have a polluted wetland, the groundwater that recharges the wetland will also be polluted,” he says.
According to Raghavan, groundwater dwelling fishes are the first to detect or sense any small changes in the water quality. “Even If there’s a small change in water parameters such as pH, oxygen levels, it will definitely have an impact on the animals that live under the ground,” he says.
Raghavan also warns, “If pollution and groundwater extraction continue without any regulation or management, we would lose a lot of species without the chance of even discovering them.”
According to Das, deeper groundwater systems in Assam and northeast India are only partially mapped and remain poorly understood beyond approximately 200?m depth. “Urbanisation, inadequate sanitation, agricultural chemicals, waste disposal and industrial or hydrocarbon activities are just some factors which add to pollution risks,” she stresses.
Ralf concludes by saying, “There is still a lot to be discovered in India, and habitats that have not been surveyed comprehensively will continue to yield surprising discoveries.”
This article is republished from Mongabay under a Creative Commons license. Read the original article here.