Kolkata, March 21, 2023

 

The scientists of the Zoological Survey of India (ZSI) have discovered a new freshwater Catfish from the North Eastern Himalaya Biodiversity hotspot in India. During an ichthyological survey conducted in the Siang River drainage in the Indo-China border areas, Drs. Pratima Singh, SD Gurumayum & Mr. S. Rath collected some specimens of the genus Exostoma under the tour party leader, Dr L. Kosygin, Officer-in-Charge of the Freshwater Fish Section of ZSI, Kolkata. After carefully examining the specimens in the Loratory the researchers identified it as a new species and described it as Exostoma dhritiae sp. nov. The new species is named after Dr Dhriti Banerjee, the first women Director of the Zoological Survey of India (ZSI) , Union Ministry of Environment & Forest and Climate Change to honour her contribution to the knowledge of the fauna of India.

The catfish genus Exostoma is characterised by having homodont dentition consisting of distally flattened oar-shaped teeth on both jaws, bilaterally separated tooth patches in the upper jaw, a continuous postlabial groove, gill openings not extending to the ventral surface of the head, and 10–11 branched pectoral-fin rays. The genus is known from the Brahmaputra River drainage eastwards to the Chao Phraya drainage in North-western Thailand.

Exostoma dhritiae is currently known only from the type locality Siking stream, a tributary of Siang River near Yingkiong (Brahmaputra River drainage), Upper Siang District, Arunachal Pradesh, India. The Siking stream is shallow, cold and swiftly flowing, with a substrate of cobbles and pebbles. The new species has some affinities with other species of the genus reported from Bhutan, China and India. However, it can be distinguished from its congeners by the condition of the posterior extremity of the adipose-fin base, the degree of tuberculation on the dorsal surface of the head, the shape of striae on the anterolateral surface of lips and other morphometric data of the body.

Before the discovery of this fish, 19 species of Exostoma were known to be valid. It is the 20th reported species of Exostoma in the world and the sixth in the Brahmaputra River basin in the North Eastern Himalayan area. It is a small hill stream fish locally known as Ngorang in Adi dialect and caught by the local tribal people for their consumption.

The paper was officially published on December 8, 2022 in Zootaxa, a mega-journal in Taxonomy published from New Zealand with Pratima Singh, L Kosygin, S D Gurumayum and S Rath as authors. (https://www.mapress.com/zt/article/view/zootaxa.5219.2.5).

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