Psilorhynchus kosygini, Shangningam, 2024

Shangningam, Bungdon, 2024, Psilorhynchus kosygini, a new species of torrent minnow (Teleostei: Psilorhynchidae) from Nagaland, north-east India, Journal of Natural History 58 (33 - 36), pp. 1293-1302 : 1294-1298

Psilorhynchus kosygini sp. n.

( Fig. 1 )

Common name. Torrent minnow.

Type material. Holotype: ZSI FF 9990, 96 mm SL; India: Nagaland, Peren district, Tepuiki River, 5 km from Poilwa village , a tributary of the Barak drainage, 25.564512°N, 93.892251°E, 155 m asl, Shangningam, 20 August 2022.

Paratypes: ZSI FF 9991, 8, 68.0–96.0 mm SL; same data as holotype.

Diagnosis. Psilorhynchus kosygini , a member of the Psilorhynchus homaloptera species group, is distinguished from all other members by the following combination of characters: 3–4 scales positioned along the mid-ventral region between the posterior base of the pelvic fin and the anal opening, body elongate with 41–42 scales along the lateral line, 14 scales in the pre-dorsal region, 8 scales around the caudal peduncle, 9–10 branched pectoral-fin rays, eye diameter 15–21% HL, head length 18.2–19.9% SL, body depth 15.6–18.3% SL, head depth 50–58% HL and vertebrae 42.

Description. Body elongate, dorsal profile arched, rising gradually from tip of snout to dorsal-fin origin, sloping steeply towards caudal peduncle. Greatest body depth at dorsal-fin origin, narrowest at caudal-peduncle base. Caudal peduncle shallow and fairly compressed. Ventral profile straight from lower jaw to anal-fin origin, with slight dorsad inclination posteriorly towards caudal-fin base. Biometric data of the specimens are shown in Table 1 .

Head large, wider than deep. Eye large, rounded, dorso-laterally located, with free orbital margin, not visible from ventral surface, situated closer to operculum than to snout tip. Mouth inferior, transverse, arched, width shorter than snout length. Barbels absent. Snout slightly rounded; its ventral surface bordered by a deep longitudinal groove on each side. Interorbital space flat, width larger than eye diameter. Gill opening narrow, extending from post-temporal region to a little beyond pectoral-fin base on ventral side. Internarial distance smaller than snout length. Nostrils large with a conspicuous rounded membranous flap between anterior and posterior openings, situated nearer to anterior margin of eyes than to tip of snout. Rostral cap fused with upper lip, separated by a shallow groove. Upper lip covered with rows of unculi. Lower jaw flattened, covered by a thick squarish cushion that can be folded backwards. Cushion composed of two adnate tissue layers: a deeper layer, the lower lip, smooth, not continuous with upper lip around corner of mouth; and a superficial layer, slightly thick, continuous with skin of isthmus, connected with rostral cap by a narrow strip of skin around corner of mouth at postero-lateralmost corner of mouth. Upper and lower jaws with sharp rasping edges. A fairly deep, distinct lateral horizontal furrow marks off mouth parts and thick rostral cap, passing on either side from post-labial groove extending anteriorly to sides of snout. Gill rakers absent. Gill membranes broadly joined to isthmus.

Paired fins horizontally placed. Pectoral fin with viii (7) or ix (1) and 7 (1), 8 (3) or 9 (4) rays, broad, expanded with rounded free margin, longer than head, almost reaching horizontal through dorsal-fin origin, almost reaching the pelvic-fin origin when adpressed. Ventral portion of dorsal fin base covered with thick skin. Pelvic-fin rays ii.7, shorter than pectoral, origin anterior to dorsal-fin origin, opposite two scales anterior to first branched dorsal-fin ray, extending beyond anus. Skin on ventral surface of unbranched pectoral and pelvic-fin rays thickened. Dorsal fin with ii.8 rays, high, tip pointed, posterior edge straight to slightly concave, much closer to snout tip than caudal-fin base. Anal fin long with ii.6 rays, almost reaching caudal-fin base when adpressed, posterior margin straight to slightly convex. Caudal fin deeply emarginate, lower lobe slightly longer than upper, principal rays 9 + 8 (8), procurrent rays 3 (3), 4(5) dorsally and 4 (5) or 5 (3) ventrally. Vertebrae 42, consisting of 29 abdominal and 13 caudal. One dissected female 76.4 mm SL with ripe ovary containing ~1250 eggs of diameter 0.5–1.2 mm.

Scales cycloid and fairly large. Lateral line feebly arched, running along middle of body with 41 (4) or 42 (4) scales,plus 2 (6) or 3 (2) on caudal-fin. Transverse scale rows from dorsalto pelvic-fin origin 4/1/3 (8), scale rows around caudal peduncle 8 (8), pre-dorsal scales 14 (8), scales between anus and anal-fin origin 13 (5) or 14 (3). Abdominal region scaleless except 3–4 scales between posteriormost pelvic fin base and anal opening.

Colouration. In 70% alcohol: body background olivaceous brown. Occiput and dorsal surface of snout brown. Scales on flanks and dorsal surface with thin melanophores, posterior edges hyaline. Mid-lateral scale dark, appearing like a dark brown lateral stripe. Ventral surface pale yellow. Anterior-most fin rays with diffuse melanophores, concentrated on fin bases. Dorsal-fin rays with thin brown melanophores, posterior margin hyaline. Paired fin rays with prominent thin brown melanophores along its interradial. Caudal-fin base peppered with dark melanophores, lower lobe with a short transverse dark band, extending to middle, margin hyaline.

In life, body background olivaceous. Ventral surface between pectoral and pelvic fins silvery white. Fin pigmentation light orange.

Distribution. Psilorhynchus kosygini is presently known only from the Tepuiki River, a tributary of the Barak River in Nagaland, India ( Figure 2 ).

Habitat. Psilorhynchus kosygini has been collected in rapids and torrential water currents ( Figure 3 ). The type locality, Tepuiki River, is cool, shaded and swiftly flowing with a gravel bottom, rocky bed substrate and numerous riffles. The species usually inhabits sandy substrate with pectoral fins spread horizontally while feeding at the bottom and adhering to rocks while at rest. Other species collected from the type locality include Balitora brucei, Neolisochilus hexagonolepis, Garra nagaensis , G. manipurensis , Schizothorax richardsonii , Devario aequipinnatus and Opsarius barna .

Etymology. The species is named after Dr Kosygin Laishram, Scientist E, Zoological Survey of India, for his contribution to the freshwater fish faunal of the Indian region.

Figures

Figure 1. Psilorhynchus kosygini: a, dorsal; b, lateral; c, ventral views.

Figure 2. Map showing the type locality of Psilorhynchus kosygini.

Figure 3. Tepuiki River, the type locality of Psilorhynchus kosygini.