The lateritic aquifers of the southern Indian state of Kerala harbour a unique assemblage of enigmatic stygobitic fishes which are encountered very rarely, only when they surface during the digging and cleaning of homestead wells. Here, we focus on one of the most unusual members of this group, the catfish Horaglanis, a genus of rarely-collected, tiny, blind, pigment less, and strictly aquifer-residing species. A six-year exploratory and citizen-science backed survey supported by molecular phylogenetic analysis reveals novel insights into the diversity, distribution and population structure of Horaglanis. The genus is characterized by high levels of intraspecific and interspecific genetic divergence, with phylogenetically distinct species recovered above a 7.0% genetic-distance threshold in the mitochondrial cytochrome oxidase subunit 1 gene. Contrasting with this deep genetic divergence, however, is a remarkable stasis in external morphology. We identify and describe a new cryptic species, Horaglanis populi, a lineage that is the sister group of all currently known species. All four species are represented by multiple haplotypes. Mismatch distribution reveals that populations have not experienced recent expansions.
Bhavania annandalei Hora 1920, is resurrected from the synonymy of B. australis (Jerdon 1849) based on examination of freshly collected topotypic specimens. The two species can be distinguished by a combination of morphological, morphometric and meristic characters, and by genetic distance using mitochondrial cox1 gene. The distribution of B. annandalei is restricted to the river systems draining the Agasthyamalai hills, below the Shencottah Gap in southern Western Ghats.
Bhavania annandalei Hora 1920, is resurrected from the synonymy of B. australis (Jerdon, 1849) based on examination of freshly collected topotypic specimens. The two species can be distinguished by a combination of morphological characters including low, dense, and sparsely distributed tubercles on dorsal surface of head and operculum, rostral barbels reaching anterior border of upper lip, rostral flaps between the rostral barbels fleshier, 11–12 scale rows above the lateral line, and caudal peduncle stout with its depth to width ratio less than 2.5. The two species formed significantly distinct clusters in multivariate space. Further, the two species have a raw genetic distance of 6.4% in the mitochondrial cytochrome oxidase subunit 1 gene. The distribution of B. annandalei is restricted to the river systems draining the Agasthyamalai Hills, below the Shencottah Gap in southern Western Ghats, while B. australis occurs in rivers north of the Shencottah Gap.
Riverscape genetics of fish, though extensively studied in temperate regions, have received limited interest in tropical rivers, especially in montane systems which not only harbour several endemic and threatened species, but are also subjected to extensive habitat modifications. We determine the population genetic structure of
The world’s largest subterranean fish was discovered in 2019, and was tentatively identified as a troglomorphic form of the golden mahseer, Tor putitora. Detailed analyses of its morphometric and meristic data, and results from molecular analyses now reveal that it is a new species of the genus Neolissochilus, the sister taxon of Tor. We formally describe the new species as Neolissochilus pnar, honouring the tribal communities of East Jaintia hills in Meghalaya, Northeast India, from where it was discovered. Neolissochilus pnar possesses a number of characters unique among species of Neolissochilus, with the exception of the similarly subterranean N. subterraneus from Thailand. The unique characters that diagnose N. pnar from all epigean congeners comprise highly reduced eye size to complete absence of externally visible eyes, complete lack of pigmentation, long maxillary barbels, long pectoral-fin rays, and scalation pattern. Neolissochilus pnar is distinguished from the hypogean N. subterraneus, the type locality of which is a limestone cave ~2000 kms away in Central Thailand, by a lesser pre-pelvic length (47.8–49.4 vs. 50.5–55.3 %SL), a shorter caudal peduncle (16.1–16.8 vs. 17.8–23.7 %SL), and shorter dorsal fin (17.4–20.8 vs. 21.5–26.3 %SL). In addition, Neolissochilus pnar is also genetically and morphologically distinct from its close congeners with a raw genetic divergence of 1.1–2.7% in the COI gene with putative topotype of N. hexastichus and 2.1–2.6% with putative topotype of N. hexagonolepis.
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