The species is only officially known from three individuals: one collected in 1936, and two collected in 1969 (without the location recorded). We're not sure why the species has vanished, but the location where the first individual was found was impacted in the 1970s by deforestation.

In 2022, Turkish ichthyologists rediscovered populations of the Critically Endangered Batman River Loach in two streams in southeast Turkey, the first time the tiny fish has been seen since 1974, and the first species rediscovered on Shoal and Re:wild’s top 10 most wanted lost fishes list, which launched in June 2021.

Populations of the Batman River loach nosedived after the construction of the Batman Dam in Turkey between 1986 and 1999, leading some scientists to fear it may have become extinct. The species’ habitat is now fragmented due to the dam, and the fish can no longer move downstream.

Local fishermen believe the Duck-billed Buntingi's decline it is related to the eruption of the nearby Colo Volcano in 1983. Invasive species have likely also played a part, and introduced diseases and parasites are also possible explanations. Overfishing has also likely caused numbers to plummet.

The fish grows up to 16 cm, though usually closer to 11cm.

It’s unsurprising that so little is known about this species: The terrain on Papua New Guinea is extremely difficult to negotiate, distances are huge, roads are few and far between, and air travel is expensive and often non-existent to remote locations. Also, the holotype was stored in the Hamburg Museum, but was destroyed during World War II.

As a pipefish, it’s closely related to seahorses. Most species of pipefish are inhabitants of tropical and temperate seas, but a few species in the Indo-Australian Archipelago are largely restricted to freshwater.

Aside from their idiosyncratic looks, pipefishes display some extraordinary behavior: females deposit their eggs on the underside of the male’s trunk, or tail, where the male incubates them for several weeks either partly or fully concealed in a pouch.

The species is so poorly known that scientists aren’t really sure of its size, but it grows to at least 15cm and possibly up to 22cm.

This species, which is also known as the Mesopotamian Barbel or Spot Barb, was once abundant, ranging from Eastern Türkiye, Eastern Syria, Iran and Iraq in the Tigris-Euphrates river system. One individual was caught in 2011, the last time this fish was scientifically documented, before it was rediscovered in 2024. Over the last three decades, however, fishing, pollution, habitat destruction and dam construction have pushed the species to the edge of extinction. Not only have several dams built in the Turkish portion of the Tigris River impacted the leopard barbel, but a new dam is under construction in Cizre, very close to where the two leopard barbels were found. 

The striking Syr Darya Shovelnose Sturgeon is endemic to the Syr Darya River, and once found in Kazakhstan, Tajikistan and Uzbekistan. It is among the smallest sturgeon species in the world, growing only up to about one foot long. It was once found in the Aral Sea, but according to NASA, the Aral Sea shrunk by more than 60% between 1973 and 2000. The Aral Sea is now hypersaline and as a result, doesn’t contain any fish, aside from in a small reservoir. The river has also experienced large levels of water extraction, damming and agricultural pollution. The sturgeon has been listed in the Red Data Book of Kazakhstan since 1978 and has also been featured on stamps.

The Titicaca Orestias is the largest member of the pupfish genus Orestias and, despite its name, it is not the only Orestias fish from Lake Titicaca. Orestias cuvieri is thought to be as old as 5 million years and is specifically adapted to its closed lake environment.

In 1937, 500,000 trout eggs were sent to Lake Titicaca, irreversibly altering the native ecosystem. There has been severe competition from introduced trout, including lake trout, brown trout, and rainbow trout, as well from Argentinian silverside from the 1930s to the 1950s. Pollutants have contaminated the water and traces of metals, such as zinc and copper have been found in the tissues of fishes. In addition, runoff from fertilizers and pesticides used in agriculture has been extremely toxic to the fish.

The Haditha cavefish is known only from a subterranean system in a sinkhole at the Sheik Hadid shrine, near Haditha, Iraq. The only way to access the system is through a well approximately five meters below the shrine. A comprehensive survey of the site in 2012 did not find the species. Water abstraction from the well itself has lowered the groundwater level, which appears to be a major threat. It is also thought that reduced groundwater levels due to water abstraction and hydrological modifications caused by the construction of a large dam near the Euphrates may have negatively impacted the site.

Until it was rediscovered in a pond at a tributary of the Tsiribihina River in late 2010, the Itasy Cichlid was only known from Lake Itasy, where it had last been seen in the 1970s. It was considered Extinct until the rediscovery.

Its coloration is jet black and the local name for the fish is ‘trondro mainty’, which translates to ‘blackfish’. 

It differs from its close relatives in having a pronounced occipital hump, even in small fishes that aren’t yet sexually mature, and in females.

The fish's population has dropped as a result of a decline in water quality due to human mediated disturbances, specifically unregulated overfishing and the introduction of invasive species into the Lake Itasy basin, which led to the swift decline of native fishes throughout the region.

What’s in a name? ‘Fat Catfish’ almost says it all. This lost fish species has more rolls than a used tire. The Fat Catfish has only ever been found 9,800 feet high in the Andes mountains, in Lake Tota, where locals call it “Pez Graso,” which can also be translated to “grease fish” — a name, perhaps, both apt and foreboding for a combustible fish. Yes, you read that right. Before the Fat Catfish became a lost species, local people sometimes burned its fat for fuel in their lamps. The mystery of their disappearance, however, remains unanswered. The Fat Catfish was described for the first time by ichthyologist Cecil Miles in 1942, and the last known individual was collected from the wild in 1957. Only nine other individuals had been recorded before then.

The Fat Catfish is also one of the top 10 most wanted freshwater fishes by the Search for Lost Fishes, the freshwater-fish focused initiative of Re:wild’s Search for Lost Species program, in partnership with Shoal.

Find out more about the Search for Lost Fishes.