Neolissochilus pnar, Dahanukar & Sundar & Rangad & Proudlove & Raghavan, 2023

Dahanukar, Neelesh, Sundar, Remya L., Rangad, Duwaki, Proudlove, Graham & Raghavan, Rajeev, 2023, The world's largest cave fish from Meghalaya, Northeast India, is a new species, Neolissochilus pnar (Cyprinidae, Torinae), Vertebrate Zoology 73, pp. 141-152 : 141

Neolissochilus pnar sp. nov.

Fig. 1

Holotype.

KUFOS.F.2022.701, 329.2 mm SL, 92 m below the surface in Krem Um Ladaw, Meghalaya, India; collected 7 Jan 2020.

Paratypes (n = 2).

KUFOS.F.2022.702, 179.7 mm, same locality as holotype, collected 21 Feb 2019; KUFOS.F.2022.703, 208.9 mm SL, Krem Chympe cave, Meghalaya, India, collected 7 Jan 2020.

Etymology.

The species name pnar, honours the ‘pnar’, the sub-tribal group of the Khasi people in the state of Meghalaya, India.

Diagnosis.

Neolissochilus pnar is distinguished from all its congeners by mandibular barbel long, reaching anterior margin of opercle (vs. short, not reaching margin of opercle). It is further distinguished from all epigean congeners by atrophied eyes, highly reduced in size in juveniles and small-adults and absence of externally visible eyes in adults (vs. presence of well-developed eyes in all life-stages); complete absence of pigmentation (vs. presence); long pectoral-fin reaching anterior base of pelvic fin (vs. short, not reaching anterior base of pelvic fin); and distinct scalation pattern with 28+2 (2) or 31+1 (1) lateral line scales, 8 scales in transverse series with 4 above the lateral line and 3 below the lateral line. Neolissochilus pnar is distinguished from the only other subterranean congener, N. subterraneus by shorter pre-pelvic length (47.8-49.4 vs. 50.5-55.3 %SL), shorter caudal-peduncle length (16.1-16.8 vs. 17.8-23.7 %SL) and shorter dorsal-fin length (17.4-20.8 vs. 21.5-26.3 %SL).

Description.

General appearance as in Fig. 1 and selected morphological characters presented in Table 3 . Body elongate, laterally compressed. Dorsal profile sharply rising from tip of snout to nape, posteriorly gently decreasing up to end of caudal peduncle. Ventral profile sloping, almost straight convex. Head large, slightly more than a quarter of standard length. Eyes tiny and highly reduced in size to a black spot or externally invisible in adults, slightly larger, but still reduced in size compared to epigean congeners in juveniles; eyes when present situated dorso-laterally, nearer to tip of snout than to posterior margin of opercle. Mouth subterminal, lips thick. Two pairs of barbels. Rostral barbel reaching midlength of maxillary barbel. Maxillary barbel long, reaching anterior margin of opercle.

Dorsal fin with 13 soft rays (iv+9), its origin almost midway between tip of snout and end of caudal peduncle, or slightly in advance. Posterior margin of adpressed dorsal fin reaching anal-fin origin. Pectoral fin with 16 rays (i+15), its length shorter than head length. Adpressed pectoral fin reaching vertical at dorsal-fin origin, and almost reaching pelvic-fin origin. Pelvic-fin with 9 rays (i+8), its origin slightly posterior to vertical at dorsal-fin origin. Anal fin with 8 rays (iii+5). Caudal fin forked with 19 principal caudal rays. Caudal peduncle 2-2.3 times as long as deep.

Body lateral line continuous, with 28-31 perforated scales, and an additional 1-2 on caudal-fin base. Transverse series with 8 scale rows, 4 scale rows between dorsal-fin origin and row of lateral line scales, 3 scale rows between row of lateral line scales and pelvic-fin origin. Pre-dorsal scales 9.

Coloration.

In life (Fig. 1A ), body white, pinkish without melanophore pigmentation. All fins hyaline. After preservation (Fig. 1B ), body beige with slight yellowish tinge. Eye, if present, visible as a black spot, larger eyes in juveniles with black iris. Some areas on the head and body of the fish appear yellow in the preserved specimens, likely due to fat deposition.

Distribution.

The species is known from the caves at Krem Um Ladaw, and the adjacent Krem Chympe in Jaintia Hills, Meghalaya, India, which drain into the Meghna River System (Fig. 2 ).

Habitat.

The entrance to the cave in Krem Um Ladaw is in the form of a large open pitch head, lies in a large, rocky, seasonally dry streambed within a forest. The entrance series is predominantly vertical with some short (<20 m) horizontal to steeply sloping sections. After descending for just over 100 m, the entrance series drops into a horizontal and relatively narrow (3-4 m) streamway, the floor of which has several pools of standing water. The cave floor is predominantly rocky with areas of bedrock, boulders and coarse gravel (Fig. 3 ). The floor of the boulder passage is mostly elevated well above water level although there are pools in places along the left wall and in lower floor sections. Debris consisting of forest vegetation is strewn along the floor indicating this area of the cave is seasonally flooded.

The fish reside in small-sized (~3m x 4m) to large (>10m x 10m) pools. Although the invertebrate community in the cave is plentiful, it is not noticeably more abundant than that of many caves in Meghalaya. Amongst the terrestrial invertebrates were brown crickets ( Eutachycines sp.), cellar spiders ( Pholcidae ) and fungus gnat larvae ( Keroplatidae ). Isopods were also frequently encountered including Cubaris sp. and Philoscia sp. Aquatic invertebrates included shrimp ( Macrobrachium cf. cavernicola ), snails ( Paludomus sp.), pond skaters ( Gerridae ), and a few tadpoles. No significant bat roosts were encountered, and therefore no guano deposits or other obvious sources of nutrients were observed within the cave. It is conceivable that seasonal flood debris (bamboo, tree branches and leaf litter) carried into the cave from the surrounding forest provides the primary food source for the fish population. There is no plant growth in the caves and in the absence of bat guano, there is probably no other primary energy source in the habitat.

Unlike Um Ladaw, the Krem Chympe, where one of the paratypes were collected, is a broadly horizontal river cave, with a massive tunnel of deep water, and various small waterfalls/dams inside. Neolissochilus pnar occurs here in pools in a side passage. The biodiversity in this cave comprises of fish ( Garra sp.), shrimps ( Macrobrachium sp.), and tadpoles. Further details and photographs of both Um Ladaw and Chympe caves are available from Candade (2022a, b).

Phylogenetic position of Neolissochilus pnar and molecular species delimitation

Phylogenetic analysis based on ML analysis revealed that the new species forms a distinct clade, and the sister taxon to a clade containing two other species of Neolissochilus , namely N. hexagonolepis ( M’Clelland) and N. hexastichus , both from the Brahmaputra River system of northeast India (Fig. 4 ). Maximum likelihood analysis of all available COI sequences of Neolissochilus (Fig. 5 ) and barcode gap analysis (Table S5) revealed that the species diversity within this genus maybe severely underestimated with multiple undescribed species. Neolissochilus pnar forms a reciprocally monophyletic clade that is also delimited as a distinct species in ASAP (Fig. 5 ). Though multiple species have been misidentified in the literature (and in GenBank) as either N. hexagonolepis or N. hexastichus , morphologically matching putative topotypes of the two nominal species (sensu Laskar et al. 2013), form clades distinct from N. pnar (Fig. 5 ). Raw genetic distance in the COI gene between N. pnar and N. hexagonolepis is 2.1 to 2.6%, and 1.1 to 2.7% between N. pnar and N. hexastichus . Neolissochilus pnar was recovered as the sister group to a clade within the ' N. hexastichus complex’ comprising sequences from Assam (MZ520668) and Nagaland (MZ617268, MZ617270, MZ618266, MZ618268, MZ618683, MZ618686, MZ620733) - the northeast Indian states neighbouring Meghalaya. Between members of this clade and N. pnar there is a genetic divergence of 0.5 to 0.8%.

Figures

Figure 1. Holotype of Neolissochilus pnar (KUFOS. F. 2022.701, 329.2 mm SL). A Immediately after capture. B In preservation. C Details of head in lateral view. D Details of head in dorsal view. E Details of head in ventral view. Yellow patches on head, body, and bases of fins represent fat deposits.

Figure 2. Collecting localities of Neolissochilus pnar in Jaintia Hills, Meghalaya, North East India. Star indicates the type locality Krem Um Ladaw, and circle indicates Krem Chympe, where one of the paratypes was collected.

Figure 3. Live images of Neolissochilus pnar in their habitat from Krem Um Ladaw (Photos A, B, C: Uros Aksamovic, D: Dan Harries).

Figure 4. Maximum likelihood analysis of Neolissochilus, Tor and Naziritor based on concatenated mitochondrial COI, cyt b and 16 S sequences. Bootstrap values based on 1000 iterations are shown along the nodes. Garra species are used as outgroup. Live specimen of Neolissochilus pnar is shown in inset (specimen not collected) (Photo: Uros Aksamovic).

Figure 5. Maximum likelihood analysis of available COI sequences for Neolissochilus with Tor putitora as outgroup. Species delimitation based on ASAP is shown as a dashed circle surrounding the phylogenetic tree. Clade containing Neolissochilus pnar is highlighted in blue. Clades containing morphologically identified putative topotypes of Neolissochilus hexagonolepis and N. hexastichus sensu Laskar et al. (2013) are highlighted in red and green respectively, with sequences generated in their original paper highlighted in blue. Neolissochilus benasi is excluded from the analysis as it does not group with remaining species of Neolissochilus (see Fig. 3). Bootstrap values based on 1000 iterations are shown along the nodes. Tor putitora is used as an outgroup.