Neolissochilus pnar grows to over 400 mm (1.3 feet) and occurs only in the limestone caves of Meghalaya, a state in northeastern India.
Neolissochilus pnar in their habitat in Krem Um Ladaw, India. Image credit: Uros Aksamovic / Dan Harries.
The newly-discovered species belongs to Neolissochilus, a genus of freshwater fish in the family Cyprinidae (commonly called the carp or minnow family).
Members of this genus are native to freshwater habitats in Asia and are often grouped with the mahseers.
“The genus Neolissochilus represents a poorly-known group of medium- to large-sized cyprinids, with currently 31 species, distributed across South and Southeast Asia,” said Dr. Neelesh Dahanukar, a researcher with the School of Natural Sciences at the Shiv Nadar Institution of Eminence, and colleagues.
“Despite its cultural and commercial importance, there have been no comprehensive studies on the taxonomy or systematics of this group since the description of the genus.”
“As a result, the identity and distribution of the majority of Neolissochilus species remains unclear.”
The new species possesses a number of characters unique among Neolissochilus species, with the exception of the similarly subterranean Neolissochilus subterraneus from Thailand.
Scientifically named Neolissochilus pnar, it completely lacks pigmentation, has long maxillary barbels, highly reduced eyes, long pectoral-fin rays, and scalation pattern.
In addition, the species is also genetically and morphologically distinct from its close congeners.
“Stories of a ‘white cavefish’ from the Siju Caves in the Garo Hills of Meghalaya, Northeast India have been documented for 100 years, but were suggested to be slightly decolorized specimens of Neolissochilus hexastichus that appeared almost white when observed inside the water, under the light of a torch,” the researchers explained.
“Only in the 1990s, a large, pale, cyprinid fish was observed in the limestone caves of the Jaintia Hills of Meghalaya, individuals of which were eventually photographed and collected in 2019, and made available for detailed scientific studies.”
“The largest individual observed in the cave exceeded 400 mm in standard length, which makes it the largest known individual of any subterranean fish in the world.”
“The largest-known subterranean fish until now is the Australian blind cave eel (Ophisternon candidum), which measures 385 mm (1.26 feet) in total length.”
“Preliminary morphological studies based on two, medium-sized specimens, revealed morphometric and meristic data similar with the golden mahseer (Tor putitora),” they added.
“However, they also showed significantly different characters including a complete lack of pigmentation and a reduction of the eye, which is small in juveniles, and completely invisible externally in adults.”
“The availability of additional fresh specimens of this unique cyprinid fish has now enabled us to study its morphological characters in more detail and to include it in a molecular genetic analysis,” they said.
“This combined evidence reveals that the world’s largest cavefish is an undescribed species of the cyprinid genus Neolissochilus.”
Neolissochilus pnar is known from the caves at Krem Um Ladaw, and the adjacent Krem Chympe in Jaintia Hills, Meghalaya, India, which drain into the Meghna River System.
“The entrance to the cave in Krem Um Ladaw is in the form of a large open pitch head, lies in a large, rocky, seasonally dry streambed within a forest,” the scientists said.
“The entrance series is predominantly vertical with some short (less than 20 m) horizontal to steeply sloping sections.”
“After descending for just over 100 m, the entrance series drops into a horizontal and relatively narrow (3-4 m) streamway, the floor of which has several pools of standing water.”
“The cave floor is predominantly rocky with areas of bedrock, boulders and coarse gravel.”
“The floor of the boulder passage is mostly elevated well above water level although there are pools in places along the left wall and in lower floor sections.”
“The fish reside in small-sized (3 x 4 m) to large (over 10 x 10 m) pools.”
“Unlike Um Ladaw, the Krem Chympe, where one of the paratypes were collected, is a broadly horizontal river cave, with a massive tunnel of deep water, and various small waterfalls/dams inside,” they added.
“Neolissochilus pnar occurs here in pools in a side passage. The biodiversity in this cave comprises of fish (Garra sp.), shrimps (Macrobrachium sp.), and tadpoles.”
Despite the ichthyofaunal richness in aquifers and caves on the Indian subcontinent, there is only a limited number of studies dealing with their diversity and distribution.
“Recent descriptions of not only new species, but also new genera and even family level taxa of freshwater fishes from the subterranean waters of India suggests major knowledge gaps in our understanding of these largely inaccessible habitats of the Indian subcontinent,” the authors said.
“Given that these habitats are also the most vulnerable to a number of anthropogenic activities, there is an immediate need to explore and understand the hidden diversity of subterranean realms in the region.”
“Description of the world’s largest subterranean fish, Neolissochilus pnar, is therefore likely to drive further explorations and understanding of this unique habitat and its remarkable fauna.”
The discovery of Neolissochilus pnar is described in a paper in the journal Vertebrate Zoology.
_____
N. Dahanukar et al. 2023. The world’s largest cave fish from Meghalaya, Northeast India, is a new species, Neolissochilus pnar (Cyprinidae, Torinae). Vertebrate Zoology 73: 141-152; doi: 10.3897/vz.73.e101011
