• Scientists in Kerala have discovered a new species of subterranean fish, which they have called the Pathala eel loach.
• The discovery would not have been possible without the help of the people in whose wells and household pipes these creatures were first spotted.
• The outcome is the result of an outreach campaign that scientists have been conducting along Kerala’s laterite soil belt since 2017.

Kochi: It was October 24, 2020. Abraham A., a small-time stage decorator and resident of Chengannur, in the Alappuzha district of Kerala, was beginning his day just like every other: with a shower. But as he stood under the water, he felt a “thread-like” thing fall from above.

When he looked down, on the pale bathroom tiles, the dark-hued ‘thread’ moved.

Abraham knew exactly what to do. He placed the wriggling creature – barely the length of his little finger – in a small glass jar filled with tap water. Then he called the “boys”, just like he had been asked to do if such a thing happened.

The ‘boys’ are research scholars at the Kerala University of Fisheries and Ocean Studies (KUFOS) in Kochi. They arrived the very next day to investigate.

It was a fish: dark pink in colour, around three centimetres long and snake-like. The researchers combed through Abraham’s overhead tank, which supplies water to his home from a 17-foot-deep dug-out well nearby. And voila! They found three more tiny fish there.

Back at the laboratory, the team examined the creature more closely. They found that its DNA revealed that it was an eel loach – a type of stream-dwelling freshwater fish found in South and Southeast Asia. Yet this one from Abraham’s well was different.

It looked like the Bhujia eel loach, a subterranean fish that dwells in underwater aquifers. The KUFOS team had discovered it in North Kerala in 2019. But some physical features – such as more vertebrae – and distinct genetic differences set the new one apart. It was new to science.

In their paper published on May 16 in the journal Zootaxa, the team christened it the Pathala eel loach (Pangio pathala). ‘Pathala’ is Sanskrit for “below the feet” – a reference to the fish’s subterranean nature.

If not for Abraham’s call, we wouldn’t know of the existence of the Pathala eel loach. According to Abraham’s wife Suja, these fish may have passed through their taps before, and they probably didn’t notice it then.

“Now we’re always on the lookout for these creatures in our wells, tanks and tap water, after the researchers told us about them,” she said.

Public awareness and people’s participation is crucial to obtain such rare ecological data – data that remains out of reach of technological advancements and whose discovery banks more on social participation.

The KUFOS researchers recognised this need while studying subterranean fish, and have been conducting workshops and door-to-door awareness campaigns along the lateritic soil belt, where such subterranean fish are usually found, of Kerala since 2017.

As a result, the people living in this region now know what to look for, and in turn scientists working here have been reporting more frequent subterranean fish sightings.

These discoveries are “exciting”, independent experts told The Wire Science, and such an effort being undertaken at the state-level is “commendable” citizen science. But there was more to it.

A world down under

Subterranean fish are tricky animals to study. First of all, they are notoriously hard to spot. They’re very small – often just a few centimetres long. So even trained eyes have a tough time spotting them, Rajeev Raghavan, an assistant professor in KUFOS’s Department of Fisheries Resource Management and co-author of the Pathala eel loach study, said.

Second, these fish dwell in underwater aquifers. They rarely venture to the water’s surface and instead tend to skulk around in crevices. So sighting subterranean fish depends entirely on chance encounters – like what happened in Abraham’s bathroom in 2020.

Most recent discoveries of subterranean fish have happened this way, in fact. That, for example, is how Raghavan and his team described the Gollum snakehead, a new species of snake-like subterranean fish, in 2019.

A fishing enthusiast had spotted the odd-looking fish in a paddy field in North Kerala after the floods of 2018. He posted a picture of it in a WhatsApp group on angling and fishing. Scientists at KUFOS heard about it and approached him for more details.

In similar fashion, another social media post led to the discovery of the Bhujia eel loach in 2019.

“Subterranean fish work is all based on opportunistic observations,” Raghavan told The Wire Science.

But once scientists get specimens in hand, the studying process is straightforward. Once they had what would later be called the Pathala eel loach, Raghavan and his team examined its physical features (morphology) under a microscope. This revealed that the fish, while similar to the Bhujia eel loach, was indeed a different species.

It had more vertebrae (67, versus 63 in the Bhujia eel loach), an additional ray (a spine-like feature that makes up a fish’s fin) on the small fin on its side, and one ray lesser on the fin next to its anus.

The team also extracted DNA from fish tissue and analysed a single gene: CO1, which scientists often use to identify fish. They found that, genetically, the new fish differed from the Bhujia eel loach by around  8% – enough to warrant its description as a new species.

The morphological diagnosis, based on a combination of characters like the fin-ray count, justifies the loach’s classification as a new species, Robin Kurian Abraham, a scientist who has been studying fish and frogs in the Western Ghats for two decades now, said. He wasn’t involved in the study.

However, Abraham added, the molecular component – referring to the genes – could have been improved by looking at multiple genes rather than relying on just one. He also said the authors haven’t specified if they used the full-length sequence or one fragment of the CO1 gene.

According to Abraham, his concern is warranted because recent studies have shown that short gene fragments don’t inform conclusions as efficaciously as full-length sequences do. “So there needs to be more caution in the use of ad hoc DNA barcoding based solely on a single gene out of thousands in an organism’s genome.”

Nevertheless, this “integrative study” – as Abraham put it – is an important step in improving the collective understanding of India’s subterranean diversity. Among other things, the findings are “certainly very exciting” because they prove the lateritic aquifers provide a substantially adequate habitat system to which diverse fish lineages – including catfish, carps and swamp-eels – have adapted.

Raghavan and his team have also been looking for more Pathala eel loaches since 2020, but they haven’t found any. They even reexamined Abraham’s well and others like it in the neighbourhood. They hope to succeed again – with the people’s continued participation.

People, perceptions, power

This ‘participation’ is the product of scientists’ efforts in Kerala since 2017. One of them was funded by the state’s Department of Environment and Climate Change. Here, a team of scientists including Raghavan and Binoy V.V., a behavioural ecologist who studies cognition and science communication at the National Institute of Advanced Studies, Bengaluru, began reaching out to people with two aims.

One, of course, was to glean more information about subterranean fish from locals, Binoy said.

The other was to dispel fears about subterranean fish. People often wrongly assumed that the brightly-colored fish are toxic, Binoy said. This would trigger misplaced alarm over their well-water being contaminated.

“So people tend to kill the fish if they find them in their wells. Many also want the fishes removed from their wells.”

The team has also conducted several workshops on the importance of conserving subterranean fish in the state. Team members approached local political parties to get larger turnouts for workshops and organised special sessions specifically for women. The latter is because, according to Raghavan, women are more likely to come across subterranean fish when they draw water from wells or work in kitchens.

The team is also in touch with local health officials – who might respond first because residents have called them to capture or kill the fish, by decontaminating wells with bleach, as soon as they spot one in their wells or sinks.

Many of these scientists have gone door to door along the laterite soil belt across Kerala, from Kasargod in the north to Thiruvananthapuram in the south. Carrying a stack of colour photographs, they have visited more than 250 houses to converse with people about the fish, how to look out for them in their tap water, tanks and wells, and whom to call when they find them.

That is how Abraham in Chengannur knew exactly what to do when he spotted the fish in his bathroom.

In fact, information on subterranean fish sightings has spiked since the team began its outreach programme.

“We’ve been receiving calls almost every week,” Raghavan said.

As a result, they have also found more individuals of the Bhujia eel loach in a new location, an irrigation channel in Kerala’s Malappuram district. This is 40 km away from its only known habitat so far.

Reaching out to locals at this level across panchayats in the state “is a commendable achievement as a citizen science initiative,” Robin Abraham said.

But these efforts have not (yet) necessarily meant that people are more accepting of these fish in their wells, according to Raghavan. “It is definitely something we hope to study and understand in the years to come.”

Include people, find species

We wouldn’t have known of the Pathala eel loach if Abraham A. hadn’t called it in.

In scientists’ pursuit of the subterranean fish of Kerala, the people on the ground play a crucial role – a specific example of an increasing acknowledgment among the community of scientists: that what they do, they don’t do alone.

So what do the locals get out of sharing their information or knowledge?

Researchers who study the process and practice of research have suggested that scientists can begin by sharing authorship on the papers they write with their local collaborators.

In line with this, Raghavan said he had asked several local residents who helped them find the subterranean fish if they would like their names on the forthcoming  papers. But no one was “keen to become part of a scientific paper,” he said.

“Instead what they wanted was recognition through local media. Most of them wanted us to talk to local reporters and ask them to do a story with the photo of the members of the household.”

The KUFOS team did this a couple of times but local reporters soon lost interest in covering the findings – especially after locals began reporting these fish in intervals less than a kilometre apart.

Abraham was not interested in being an author on the species description of the Pathala eel loach either.

“That’s not necessary,” he said. “I wanted to inform them when I came across the fish, that’s all.”