Turkish scientists find the ‘lost’ Batman River Loach

When Turkish scientists Cüneyt Kaya and Münevver Oral set out to find the Batman River Loach, they weren’t sure what to expect. The endangered freshwater fish had not been seen in almost 50 years, despite decades of search efforts by local and international ichthyologists. So, when Kaya, a fish taxonomist at Recep Tayyip Erdogan University, and Oral, a geneticist and research fellow at the same university, found the tiny yellow-and-brown striped fish on the first day of their expedition, they almost couldn’t believe it.

A lucky first catch

“It came straight up to us the first time that we were in the river,” says Oral. “We were super surprised and really happy.”

The fish, which was once found in streams and tributaries of the Batman and Ambar River in Southeastern Turkey, hadn’t been seen since 1974. And it’s the first to be rediscovered by Shoal and Re:wild’s Search for Lost Fishes.

“At first, we didn't realize what was going on because this species is quite similar to some other species that inhabit the same river,” explains Oral. “But as soon as Cüneyt saw it, he said, ‘Okay, that looks a little different.’”

Within a few hours, the team were able to confirm what they hoped: they had found the Batman River Loach.

A first for the Search for Lost Fishes

Kaya and Oral were inspired to look for the elusive species after learning about the Search for Lost Fishes, a global initiative by Shoal and Re:wild. The Search for Lost Fishes is initially focusing on 10 species from a list of more than 300 that the IUCN Freshwater Fish Specialist Group, the world’s leading authority on freshwater fishes, identified as missing to science.

The Search for Lost Fishes is also coming at a critical time for freshwater species. In February 2021, a global report on freshwater fishes, written by 16 conservation organizations including Re:wild and Shoal, found about one third of populations are at risk of extinction. Eighty species have been declared Extinct and 16 of those extinctions were in 2020.

“Despite the fact that fish have been sort of neglected by traditional conservation, they are really important to millions of people across the world,” says Mike Baltzer, executive director of Shoal. “People often aren’t aware of the incredible diversity that’s underneath the surface.”

To find the long-lost Batman River Loach, Shoal reached out German fish taxonomist Jörg Freyhof, who suggested Kaya lead the effort. Kaya, who was familiar with the freshwater fish species in Turkey, especially in upper Tigris River from previous field work, gladly accepted the challenge.

While previous searches for the river loach had focused downstream of the Batman dam, where the fish had been spotted in the 1970s, Kaya and Oral narrowed their search to the shallow, fast-flowing waters upstream of the dam. They had already done some work at the outflow just below the dam, but this was their first survey in the upper reaches of the river.

Shifting the search

Kaya and Oral suspected the species had a better chance of surviving above the dam because the structure fragments the fish’s habitat. The Batman River Loach is one of the smallest loach species in the world at around an inch-and-a-half long, which meant the team had to use special tight-weave nets to make sure the loach didn’t slip through undetected.

Another challenge the team faced was confirming that the tiny fishes they found were, in fact, the Batman River Loach.

“I understood that these loaches were different from the others I had seen before, but I could not immediately understand which genus they belonged to,” explains Kaya.

One key feature that separates the species from four other loaches in the area is their vertical striping.

“I was very excited when I saw the distinctive bands in the last individual I caught towards the end of the study in the creek,” says Kaya. “I immediately opened my laptop and looked at the original drawing of the Batman River Loach.”

It seemed like a match, but Kaya wanted to know if other ichthyologists agreed. Next, he sent a picture to Freyhof, who confirmed that he agreed: it had to be the Batman River Loach.

During their nine-day expedition in October 2021, Kaya and Oral found 14 Batman River Loaches in the Sarim Stream and nine more in the Han Stream.They also met with local residents, including some who have reported seeing a fish resembling the Batman River Loach. Because it’s incredibly difficult to distinguish between loach species in the area, explains Kaya, the fish can be easily misidentified.

Fish in troubled waters

Though scientists say more research is needed to determine threats to the fish, they blame the dam, pollution, and recent droughts for the species’ near disappearance. When the dam shuts off water flow, Kaya explains, it cuts off the fishes’ access to food, new habitat, and breeding grounds. The fact they found nearly two dozen loaches is a clue that the species has managed to survive despite these threats, but the population is fragile.

“While the species is doing better than I expected, we cannot say that the species is not threatened,” says Kaya. “We think the species is restricted to the upper part of the dam, and only in a few streams.”

Another threat to the species is drought, which has been exacerbated by climate change in recent years. When Kaya was searching for the species, he was surprised to see certain tributaries of the river were dry for the first time given his 12 years of experience working in Anatolia.

While a tiny fish like the Batman River Loach may seem like an inconsequential species to lose, the rediscovery is a reminder that every member of an ecosystem matters.

“As a geneticist, I hear, ‘It's a little fish, why do you bother?’” says Oral. “But it’s not that simple. We can’t say that if we lose the species, it doesn’t matter—there’s no such a thing in biology.”

The loach may be small, she says, but its role in the ecosystem shouldn’t be underestimated.

Conserving the Batman River Loach

Next, Kaya and Oral plan to look for the fish in other streams and rivers in the region to better understand where Batman River Loaches have managed to survive, and how to best protect the species.

The pair also have their eyes set on another of the Top 10 Most Wanted Lost Fishes native to Turkey, the Mesopotamian Barbel, and hope they’ll be as lucky.

“We need to know what is lost, therefore we can find it,” says Kaya.