A new genus of freshwater fish discovered in Western Ghats 

The nemacheilid loaches – Mesonoemacheilus remadevii and Nemacheilus monilis – were misclassified until now and have now been classified under genus Koima, which is distinguished from other Western Ghats and Indian subcontinent nemacheilids based on a combination of characters

A team of researchers have discovered Koima, a new genus of freshwater fish endemic to the Western Ghats encompassing two known species that were previously assigned under the genus Nemacheilus.

While its discovery highlights the importance of Western Ghats as a biodiversity hotspot and a centre of endemism, it also underscores the need for a comprehensive taxonomic revision of many freshwater fish groups including nemacheilid loaches. The new genus was described by V.K. Anoop and Rajeev Raghavan, of Kerala University of Fisheries and Ocean studies (Kufos), and Neelesh Dahanukar, of Shiv Nadar Institution of Eminence, Delhi.

The research published in the leading international taxonomy journal Zootaxa points out that the Western Ghats’ endemic loach diversity remains largely unexplored and a taxonomic investigation using integrated approaches could uncover new species and genera within this biogeographic region.

The family Nemacheilidae includes a diverse group of freshwater fish found mostly in tropical Asia and Europe and many species are valued both as a food source for local communities and as popular ornamental fish. According to the researchers, “understanding ‘species boundaries’ in closely related Nemacheilid species has been a long-term challenge, given their small size, complex ontogenic colour variations, and morphological plasticity.” They say Koima is distinguished from all other genera of family Nemacheilidae by its “unique colour pattern comprising a yellowish-brown ground colour, single row of black spots on lateral line, all fins hyaline, and absence of a uniform banding pattern on dorsal side.”

The study employed an integrative approach to re-evaluate the taxonomic status of two enigmatic nemacheilid loaches of the Southern Western Ghats: Mesonoemacheilus remadevii and Nemacheilus monilis. The research showed that both species were misclassified until now and require placement in a new genus. Koima, the new genus is distinguished from other Western Ghats and Indian subcontinent nemacheilids based on a combination of characters.

Specimens for this study were collected from the Kunthi, Bhavani, Moyar, Kabini, and Pambar rivers in the Western Ghats.

Distinct character

Koima remadevii typically inhabits swift-flowing riparian streams with substrates comprising rocks, boulders, and gravel, with sand and silt patches scattered throughout. These substrates produce a variety of microhabitats, such as gaps under boulders, and clefts between rocks that provide protection from powerful currents. Koima remadevii thrives in fast-flowing streams with rocky substrates. These fish seek shelter in the gaps between rocks and beneath boulders, finding protection from strong currents. Currently, Koima remadevii is only known from its type locality in the Kunthi river inside Silent Valley National Park.

Meanwhile, Koima monilis inhabits various tributaries of the Cauvery river, occupying microhabitats ranging from large rivers to small, fast-flowing streams at elevations between 350 and 800 m. The generic name, Koima is derived from Malayalam and is the vernacular word used for loaches.

Published - November 15, 2024 07:39 pm IST