First record of Garra birostris Nebeshwar & Vishwanath, 2013 (Cypriniformes: Cyprinidae) from Doyang and Dikhu rivers of Brahmaputra drainage, Nagaland, India

: Garra birostris is recorded for the first time from the Doyang and Dikhu tributaries of the Brahmaputra drainage, Nagaland, northeastern India. The detailed morphometric and meristic data of the specimens that forms the basis of this new record are presented.

ISSN 0974-7907 (Online); ISSN 0974-7893 (Print) Members of the labeonine genus Garra Hamilton, 1822 are widely distributed from Sub-Saharan Africa to Borneo through the Arabian Peninsula, southern, and southeastern Asia, and southern China (Zhang & Chen 2002). The genus Garra is diagnosed in possessing a specialized adhesive pad or modified lower lip forming a gular disc, that displays extraordinary variations in the snout (Kottelat 2020a). They can also be distinguished by their pharyngeal teeth arranged in three rows, the origin of dorsal fin which starts slightly anterior to pelvic fins, and an anal fin originating well behind the pelvic fins (Stiassny & Getahun 2007).

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as well as in neighbouring Bhutan (Thoni et al. 2016). The present study records for the first time the occurrence of Garra birostris from two major river systems of Nagaland state-Dikhu and Doyang-are tributaries of the Brahmaputra.

Materials and Methods
Specimens were collected from the Doyang (26.0605 0 N, 94.0005 0 E) and Dikhu rivers (26.4506 0 N, 94.7033 0 E) of the Brahmaputra drainage, in Nagaland, India ( Figure 1). Specimens were fixed in 10% formalin on site, and subsequently transferred to 70% ethanol for permanent storage. All measurements were recorded to the nearest 0.1 mm using digital calipers including the first non-zero digit from the left, through the last digit. Meristic and morphometric data followed Kottelat (2000b) and Nebeshwar & Vishwanath (2013). Gular disc terminology followed Kottelat (2020a). Meristic data were taken under a Leica M205A stereo-zoom microscope. ArcGIS tool was used to map the spatial distribution of specimens (ESRI 2017). Specimens are deposited at the Zoological Survey of India (ZSI), Kolkata and Nagaland University Fish Museum (NUFM), Nagaland.

Results
Specimens were identified as Garra birostris primarily based on the presence of a prominent, bilobed proboscis, bearing large, tri-to tetra-cuspid acanthoid tubercles on each lobe, a transverse lobe with small to large acanthoid tubercles, deep transverse groove, a black spot at the upper angle of gill opening and six lateral black stripes on the caudal peduncle (Image 1,2). Meristic and morphometric data are presented in Table  1. Dorsal fins with two simple and, 8½ branched rays. Pectoral fin with one simple and, 12-15 branched rays. Pelvic fin with one simple and 8 branched rays. Anal fin with two simple and 5½ branched rays. Predorsal scales 10-11. Lateral line complete with 33-34 scales. Circumpeduncular scales rows 16. Transverse scale rows above lateral line scale 4½, and, between lateral line and pelvic-fin origin 3½.

Distribution and Habitat
Previously known only from the rivers in Arunachal Pradesh (Nebeshwar & Vishwanath 2013), Assam (Basumatary et al. 2017), andBhutan (Thoni et al. 2016), this study extends the distribution of the species into the Doyang and Dikhu rivers of Nagaland. Garra birostris tends to inhabit swiftly-flowing sections of headwaters and tributaries of large river systems, but also occurs in some wider, lowland river channels, as well as reservoirs. Ideal habitats comprise clear and slightly basic (pH: 7.5-8.08), oxygen-saturated water (10.02-11.38 mg/l) with a total hardness (82.39-72.52) and total dissolved solids under the desirable limits of 500 mg/l.

Discussion
Members of the genus Garra shows varied snout morphology (Nebeshwar & Vishwanath 2017). Garra birostris specimens collected as part of the present study belonged to group possessing a snout with proboscis (bi-lobed) and a prominent transverse lobe as described by Nebeshwar & Vishwanath (2017). Garra birostris is rheophilic cyprinid with a flat belly and the lower lip expanded at its posterior rim to form an oval sucking pad and a greatly diminished vomero-palatine organ.

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Garra biloborostris (Roni & Vishwanath, 2017) and Garra chathensis (Ezung et al., 2020b) are the closest congeners of Garra birostris as they belong to the 'proboscis species-group' with a prominent bilobed proboscis (Nebeshwar & Vishwanath 2017). The presence of large tri-or tetra-cuspid acanthoid tubercles on each lobe in G. birostris, three acanthoid tubercles on each lobe in G. biloborostris, and large bicuspid acanthoid tubercles on each lobe in G. chathensis are the most important characters distinguishing the three species.
In the present study, G. birostris was identified based on the large, tri-to tetra-cuspid acanthoid tubercles on each lobe, having 4½|1|3½ transverse scale rows and a black spot at the upper angle of the gill opening. Our specimens of G. birostris differed to a certain extent in the characters mentioned in the original description in having fewer dorsal fin ii8½ (vs iii8½) and anal fin rays ii5½ (vs iii5½) which may be to the result of differences in habitat physio-chemistry and climatic conditions.
The first record of G. birostris from Nagaland, adds yet another species to Nagaland's ichthyofauna. This species is locally known as Aaghungu in Sumi Naga dialect, Angad in Ao Naga dialect and Engoro in Lotha Naga dialect. The prevailing threats to the fish species and their habitat occur mostly due to over exploitation including using destructive fishing methods, various anthropogenic activities hazards, such as irrigation water for human needs and plastic waste discharge, and sand & boulder mining. Public awareness campaigns among the general public could be the most effective step toward preserving and conserving native fisheries resources. Anthropogenic activities must be regulated, especially those negatively impacting aquatic ecosystems and their resources. It is also necessary to conduct continued research to investigate and document the ichthyofauna in this region, especially from poorly-explored tributaries, as to develop sustainable exploitation and for conservation plans for the fish fauna.

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