ABSTRACT
Two new species of fishes are described from the tributaries of the Brahmaputra River in Nagaland, Northeast India. Glyptothorax sentimereni, described from the Dikhu River, is distinguished from congeners in having the following combination of characters: ventral surfaces of pectoral spine and first pelvic-fin ray with plicae, serrated posterior edge of dorsal-fin spine, thoracic adhesive apparatus completely encinctured by striae, length of dorsal-fin spine 13.7–16.1% SL, body depth at anus 17.1–19.6% SL, length of dorsal-fin base 12.0–13.1% SL, post-adipose distance 20.8–22.2% SL, head depth 16.5–17.0% SL and dorsal-to-adipose distance 21.8–23.5% SL. Oreichthys elianae, described from the Tsurang River, is distinguished from its congeners by a combination of characters that include 19+1 scales (with 5 pored scales) in longitudinal series, ½3/1/2½ scales in transverse row, 9 predorsal scales, 14–15 pores on cheek, a black spot on the caudal-fin base, and reddish fins.
INTRODUCTION
Nagaland, one of the eight states that make up the Northeastern region of India is drained by three major rivers, viz., the Brahmaputra, Chindwin and Barak. This region is recognized as an exceptional hotspot of freshwater biodiversity (Kottelat & Whitten, 1996) due to its unique biogeographic setting between the Eastern Himalaya and Indo Burman ranges. While there have been efforts to document the biodiversity of the state including orchids (e.g. Deb et al. 2003, 2019 & 2021), amphibians (e.g. Ao et al., 2003 & Biju et al., 2019), beetles (Ghosh et al., 2020 & Mozhui et al., 2020), and butterflies (e.g. Naro & Sondhi, 2014), freshwater fish have been poorly studied and documented. The earliest known ichthyological surveys in Nagaland were carried out by Hora & Mukerji (1935) and Hora (1936), with the majority of their sampling sites focused in the Manipur Valley of the 1930s (particularly the Naga Hills, comprising parts of present-day Nagaland and Manipur States). These early surveys resulted in the description of Psilorynchus homalptera (Psilorhynchidae) and Bangana devdevi (Cyprinidae). Since then, there have been no systematic and comprehensive ichthyological surveys in Nagaland. However, surveys in the recent past have resulted in new species discoveries (see Shangningam & Singh, 2020; Praveenraj, 2023; Shangningam, 2024; Kechu & Pankaj, 2025).
During recent ichthyological surveys in the tributaries of the Brahmaputra River in Nagaland, several specimens belonging to the genera Glyptothorax and Oreichthys were collected. Detailed morphological studies and comparisons with congeners indicated that these specimens are new to science, which are described here as Glyptothorax sentimereni sp. nov. and Oreichthys elianae sp. nov.
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