World's 'most wanted' fish rediscovered after 50 years

A Critically Endangered species of fish has been recovered after vanishing for almost five decades. 

Since being first described in the 1970s, the Diyarbakir loach had been lost to science after researchers were unable the relocate the fish in its Turkish habitat. The construction of a large dam on the river in the 1980s and 1990s sliced the fish's habitat in two, leaving it isolated in remote stretches of the waterway. 

However, the fish has now been rediscovered thanks to the efforts of scientists from Recep Tayyip Erdogan University, who led a successful search for the species. 

Dr Cüynet Kaya, an associate professor who helped rediscover the loach, says, 'After finding the specimens, it seems that our lost fish has managed to survive despite the threats in the environment. It is now essential to conduct a detailed field study in the region in order to determine the species' population density and distribution area.  

'These data will play a key role in the correct determination of the conservation status of the species. We took the first step by finding this lost species – now is the time to act to protect it.' 

The drive to find out the species' fate was driven by the Search for the Lost Fishes programme by fish conservation organisations Shoal and Re:wild, a non-profit launched by actor Leonardo DiCaprio. 

Hunting a ghost 

The Diyarbakir loach was first discovered in 1974 in the Batman River from just two locations along the waterway and its tributaries. It is a small fish measuring around 3.5 centimetres at its largest, and at the time was considered to belong to another already known species. 

It would not be until almost two decades later when in 1998 the specimens were recognised as a new species, Paraschistura chrysicristinae. However, no other specimen of the loach had been seen since its first discovery, with fresh searches for the fish turning up no results. 

In its absence, the species was classified as Critically Endangered by the International Union for the Conservation of Nature (IUCN), with notes suggesting the species may have become extinct given the continuing lack of sightings.  

Efforts to rediscover the species were complicated by the construction of the hydroelectric Batman Dam in 1999, which cut the fish off from much of its original range. While the generation of clean power can have benefits, dams alter how rivers behave and can cause significant environmental damage. 

Cüynet says, 'The species' preferred habitat is shallow streams, with medium or fast flowing stones or gravel. It is obvious that the establishment of the dam caused shifts in biodiversity due to degradation of the lower part of the habitat needed by the species.' 

In recent years, it seemed as though the Diyarbakir loach would become a footnote in ichthyology, a species lost in the midst of time. However, with the species named as one of ten 'most wanted' lost species by Shoal, there was a renewed impetus to try and find the fish. 

Previous searches had focused on the areas south of the dam, where the species was originally found. However, Cüynet and colleague Dr Münevver Oral decided to investigate to the north, where the fast-flowing streams still persist. 

Heading to the Sarim and Han streams, the researchers were finally rewarded with sightings of the small yellow- and brown-striped fish. In total, they found 23 individuals. 

Describing the moment they found the fish, Cüynet says, '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.  

'I immediately opened my laptop and looked at the original drawing of the Diyarbakir loach and experienced that elusive happiness of meeting one of the 10 most wanted fish species in the world.' 

Back from the brink? 

As some had presumed it was extinct, the Diyarbakir loach can be considered an example of a 'Lazarus species', named for the Biblical figure who rose from the dead.   

James Maclaine, Curator of fish at the Museum, says, 'A Lazarus species is something that has been considered to be extinct and has then been rediscovered later. The coelacanth is probably the most famous example in fish. It was thought to have gone extinct around 65 million years ago but was found in 1938 by Marjorie Courtenay-Latimer. It was like finding a dinosaur that was still alive.

'It's more likely that marine rather than terrestrial animals can become a Lazarus species, as it's much more difficult to explore the entire ocean. You have to be careful when declaring a marine species extinct as it's difficult to say for sure that it's not left somewhere.  

'Freshwater animals, however, are normally gone once they stop being found. I was involved in the hunt for a freshwater blenny species in Cyprus of which the Museum holds the only specimens. These specimens are the only evidence of its existence there, which was enough for researchers to try and find it, but sadly there were no sightings.' 

Despite not having been officially recorded for half a century, the researchers suggest that the loach may have been found before but simply misidentified. This is because it turns out that the Diyarbakir loach's stripes disappear after capture, which they presume is a result of stress.  

Now the Diyarbakir loach has been recovered, the race is on to confirm the status of the other nine 'most wanted' fish, including the duck-billed bunting, the Haditha cavefish and the fat catfish.