Cabdio crassus, Lalronunga & Singh, 2019

Lalronunga, Samuel & Singh, Mahender, 2019, Cabdio crassus, a new species of cyprinid fish (Teleostei: Cyprinidae) from the Kaladan River of Mizoram, India, Zootaxa 4657 (1), pp. 159-169 : 162-164

Cabdio crassus , sp. nov.

( Fig. 2 )

Holotype: ZSI FF 8218, 88.1 mm SL; India; Mizoram, Kaladan River, in the vicinity of Kawlchaw village; 23°28’29”N; 92°23’27”E; Lalramliana et al., 24 Nov. 2015.

Paratypes: ZSI FF 8219, (2), 91.2–94.4 mm SL; PUCMF 17017 (5), 85.8–111.4 mm SL ; PUCMF 17018 (3), 90.0– 95.5 mm SL; (dissected and preserved in glycerin with thymol) data as holotype .

Diagnosis. Cabdio crassus markedly differs from all other valid species of Cabdio ( Fig. 3 ) by having the venter keeled from mid-point of chest, between the posterior base of the pectoral fin and along the abdomen up to the anus, and possessing 11½–12½ (vs. 7–9) branched anal-fin rays. It is further distinguished from C. morar and C. ukhrulensis by possessing more lateral-line scales (45–51 vs. 38–42 in C. morar and 35–37 in C. ukhrulensis ), more predorsal scales (20–23 vs. 17–18 in C. morar and 14 in C. ukhrulensis ) and more lateral transverse scales (½7/1/3½ vs. 5/1/ 2 in both C. morar and C. ukhrulensis ). It also differs from C. jaya in having fewer lateral-line scales (45–51 vs. 52–60), more lateral transverse scales (½7/1/3½ vs. 5/1/3) and more pharyngeal tooth-rows (3 vs. 2).

Description. See Table 1 for morphometric data and Figure 2 for general appearance. Body elongate, laterally compressed, body depth greatest at dorsal-fin origin. Dorsal profile rising from tip of snout to dorsal-fin origin, then gradually sloping towards caudal peduncle. Ventral profile convex up to caudal peduncle; dorsal and ventral profile of caudal peduncle slightly concave. Chest and abdomen keeled from mid-point of chest between posterior base of pectoral fin through abdomen till anus. Head compressed along entire length; depth greater than width.

Eye ovoid, located in anterior half of head, visible in both dorsal and ventral view. Snout rounded with cluster of tubercles; its length equal to eye diameter. Mouth subterminal, rictus not reaching vertical through anterior margin of orbit. Barbel absent.

Dorsal fin with 2 (15) unbranched and 6½ (1) or 7½ (14) branched rays, its origin at vertical through posterior base of pelvic fin, posterior margin slightly concave. Pectoral fin with 1 unbranched and 12 (3), 13 (9) or 14 (3) branched rays, adpressed fin tip reaching two-thirds distance between its origin and pelvic-fin origin, axillary scale present at its base. Pelvic fin with 1 unbranched and 7 (15) branched rays, adpressed fin tip reaching midway between its origin and anal-fin origin, axillary scale present at its base. Anus closer to anal-fin origin than to base of last pelvic-fin ray. Anal fin with 3 unbranched and 11½ (2) or 12½ (13) branched rays. Caudal fin forked, with 10 + 9 (15) principal caudal-fin rays, its lobes more or less equal.

Lateral line complete, prominent, curved, with 45 (2), 46 (6), 47 (3), 49 (1), 50 (2), 51 (1) on body plus 1 or 2 scales on caudal-fin base; ½7/1/3 (4) or ½7/1/3½ (11) scales in transverse line from dorsal-fin origin to pelvic-fin origin. Circumpeduncular scales 16 (15), predorsal scales 20 (3), 21 (3), 22 (7) or 23 (2), pre-pelvic and pre-anal region scaled. Five infraorbital bones ( IO 1–5); IO 3 largest, deep, partly overlapping preoperculum; post cleithrum absent; 3 rows of pharyngeal teeth. Vertebrae (abdominal + caudal): 24 + 16 = 40 (1) or 25 + 15 = 40 (1).

Colouration. ( Fig. 2 ) Dorsum brownish, lighter towards flank. Lower half of body and belly silvery or pale white. Caudal fin hyaline with black pigment distally. Other fins hyaline without markings.

Geographical distribution. Known from the main channel of the Kaladan River drainage of Mizoram, India ( Fig. 5 ).

Etymology. The specific name crassus is a Latin adjective meaning stout or thick, referring to the stout or thick body in comparison with other species.

Molecular analysis. In the coi tree, Cabdio crassus is nested within Cabdio (interspecies distance ranges from 7.8 to 12.3%) ( Fig. 1 ). The genetic distance between Cabdio crassus and C. morar is 11.7–12.3%, and between it and C. ukhrulensis is 7.8–8.0%. The inability to collect fresh specimens results in non-availability of tissue sample in the case of C. jaya .

Identity of Cabdio reported in GenBank. Analysis of the generated Cabdio sequences with close species available in the GenBank revealed several potentially misidentified specimens ( Table 3 ). Our 7 developed sequences of Cabdio morar (morphologically identified through a thorough comparison of specimens from ZSI, Kolkata and ZSI, Shillong: see Comparative Material, below) clustered in the ML tree with GenBank sequences labelled Salmostoma bacaila (downloaded from the NCBI KT 364775 , KX266823 , EU417785 , EU417786 , EU417789 , KJ936881 , KJ896723, KJ896724 and JN815302 ) with 0.0–1.2 % K2P distance, indicating that these GenBank sequences in fact represent Cabdio morar . Further, the calculated genetic distance between Cabdio morar and the species labelled as Salmostoma sp. ( JX 260968 , JX 260969 ), which is 2.0–3.0%, and between C. morar and Salmostoma sp. ( KY 290071 ), which is 4.4%, suggested that the latter two may represent species of Cabdio , rather than to Salmostoma . Our sequences of Cabdio ukhrulensis show a very low genetic distance (0.0–0.2%) and cluster together in the ML tree with GenBank sequences labelled C. morar ( AP 011335 , KJ 909343 and KJ909344 ) indicating that they too, are conspecific. Furthermore, the GenBank sequences labelled as Aspidoparia morar ( FJ 459447 ) and A. jaya ( FJ 459446 ) clustered together with Salmostoma bacaila ( HM 224244 , MG 954366 , NC015549, KY290072 , KY290087 ) with a low genetic distance of 0.3–0.7 % indicating that they represent the latter species.

Figures

FIGURE 1. Maximum Likelihood (ML) tree of coi dataset of 39 sequences using K2+G+I nucleotide substitution model with 1000 bootstraps

FIGURE 2. Cabdio crassus ZSI FF 8218, holotype, 88.1 mm SL; India, Mizoram, Kaladan River

FIGURE 3. Image of other Cabdio spp. A) Cabdio jaya, ZSI FF 5607, 74.3 mm SL; India, Arunachal Pradesh. B) C. morar, ZSI FF 4968, 70.6 mm SL; India, West Bengal, Ganga River. C) C. ukhrulensis, PUCMF 15054, 72.7 mm SL.

FIGURE 5. Drainage Map showing the locality of Cabdio crassus sp. nov. (▲) and the distribution of the genus Cabdio examined in this study.