New genus and species of blind miniature fish discovered in Assam

An international team of researchers from Germany, India, and Switzerland has discovered a remarkably strange new species of fish living in a hand-dug well in a village in Assam. This discovery of Gitchak nakana is a major milestone for science, as it marks the first time an aquifer-dwelling fish has been documented in Northeast India or the Eastern Himalayan region.

The findings were published recently in Scientific Reports, a nature portfolio journal. The scientific team comprised of Ralf Britz and Amanda Pinion (Senckenberg Museum, Dresden, Germany), Rajeev Raghavan (Kerala University of Fisheries and Ocean Studies (KUFOS), Kochi), Wimarithy Marak and Kangjam Velentina (Assam Don Bosco University, Guwahati) Yumnam Lokeshwor (Dhanamanjuri University, Manipur) and Lukas Rüber (Natural History Museum, Bern, Switzerland).

No skin pigment

The new species has been named Gitchak nakana, drawing from the Garo language to describe its appearance. “Gitchak” means red, while “na-tok” and “kana” refer to absence of eyes. This tiny fish, which grows no larger than two centimeters, belongs to a new genus within the loach family but differs from all other members of the family Cobitidae by a number of unique characters. Because it lives deep underground in water-bearing rock layers, it is completely blind with no visible eyes. Its body is translucent and lacks any skin pigment, which causes its blood to show through and gives the fish a striking, bright red appearance.

The most bizarre biological feature of this new species is the complete absence of a skull roof. In a departure from almost all other bony fish, the top of its brain is covered only by skin rather than bone. This structural rarity, combined with its miniature size, makes it an evolutionary enigma. Scientists believe this discovery proves that the groundwater systems of Northeast India harbor a highly specialised and hidden world of wildlife that was previously thought to exist only in the southern parts of the country.

Because the fish has only been found in a single well in very small numbers, the researchers are keeping its exact location a secret. They are concerned that disclosing the site could lead to illegal collection for the international aquarium trade, which has already threatened other rare cavefish in neighbouring Meghalaya. “Surprisingly, the cave mahseer from Meghalaya, Neolissochilus pnar, has recently been available in the international aquarium pet trade, although a better understanding of its population size, wider distribution and potential threats to its habitat is still lacking. However, such information would be essential to plan conservation prioritisation and action for a subterranean fish with such a restricted distribution,” said Dr. Raghavan, who is also the South Asia Chair of the IUCN SSC Freshwater Fish Specialist Group.

Experts believe that consistent, long-term study of these fascinating animals is certain to lead to the discovery of many more species currently unknown to science. “The subterranean fish research group led by Dr. Raghavan at KUFOS has been credited with some of the most interesting discoveries of groundwater-dwelling fishes of the Indian subcontinent, including Neolissochilus pnar – the world’s largest cavefish. The group has also described four subterranean fish species and one blind subterranean shrimp from various parts of Kerala. Subterranean fishes are one of the most enigmatic and evolutionary distinct groups of fishes worldwide. As a national hub for groundwater and subterranean fish research, KUFOS has made significant contributions to our understanding of these rare and poorly-known taxa, through an innovative citizen-science programme and extensive international collaborations,” said A. Biju Kumar, Vice-Chancellor of KUFOS.