Pethia rutila, Marcus Knight, J. D. & Laltlanhlua, Zathang, 2014

Marcus Knight, J. D. & Laltlanhlua, Zathang, 2014, Pethia rutila (Teleostei: Cyprinidae), a new species from Mizoram, Northeast India, Zootaxa 3827 (3), pp. 366-374 : 367-370

Pethia rutila , sp. nov.

( Fig. 2 A, B)

Holotype: ZSI FF 5215, 44.6 mm SL; India; Mizoram, Aivapui River, in the vicinity of Phuldungsei Village; 23°28'29"N; 92°23'27"E; Lalramliana et al., 3 March 2014.

Paratypes: ZSI FF 5216 (3), 33.3–40.2 mm SL; PUCMF 14004 (5), 33.7–40.9 mm SL; India, Mizoram, Keisalam river, a tributary of the Karnaphuli River, in the vicinity of Phuldungsei Village; 23°31'23"N; 92°22'38"E; Lalramliana et al., 6 March 2014. PUCMF 14005 (3), 39.9–45.3 mm SL; data as for holotype. PUCMF 14006 (3), 31.2–44.8 mm SL; (dissected and preserved in glycerin with thymol) Mizoram, Keisalam River, a tributary of the Karnaphuli River, in the vicinity of Phuldungsei Village; 23°31'23"N; 92°22'38"E; Lalramliana et al., 6 March 2014.

Diagnosis. Pethia rutila is distinguished from all its congeners in the Ganges-Brahmaputra drainage, Kaladan drainage and the Chindwin-Irrawaddy drainage (with the exception of P. expletiforis , P. macrogramma , P. stoliczkana and P. tiantian ) in having a complete lateral line. It is distinguished from all its congeners by the combination of the following characters: a black caudal-peduncle blotch extending over scales 16–18 or 17–19 of the lateral line centered above the insertion of the last anal-fin ray; an inconspicuous black humeral spot on the scale row below the 3rd and 4th lateral-line scales; 8 or 9 predorsal scales; 4½ scales between dorsal-fin origin and lateral line, and 3½ scales between lateral line and pelvic-fin origin.

Description. See Table 1 for morphometric characters, and Figure 2 for general appearance. Head short, deep, its length about one-fourth SL, its depth slightly more than three-fourths its length; body elongate, laterally compressed, its maximum depth slightly less than half its standard length. Dorsal profile rising from tip of snout to origin of dorsal-fin, then sloping gently from dorsal-fin base to caudal-fin base; body depth greatest at dorsal-fin base. Ventral profile slightly curved to chest; abdomen profile straight upto anal-fin origin; caudal-peduncle profile slightly concave, its least depth a little less than its length.

Eye ovoid, moderately large, located in anterior half of head, its diameter about one-fourth head length. Snout rounded, its length less than eye diameter, devoid of tubercles. Mouth subterminal, rictus not reaching vertical through anterior margin of orbit. Barbels absent, lips thick, lateral fold on snout present.

Dorsal-fin with 2 (1) or 3 (14) unbranched and 8 branched rays (15), its length equal to head length, its origin slightly posterior to pelvic-fin origin, above 9th lateral-line scale; last unbranched ray posteriorly serrated, with 12–14 serrae; first branched ray longest; posterior margin straight or slightly concave. Pectoral-fin with 1 unbranched and 12 (9) or 13 (6) branched rays, fourth and fifth branched rays longest, adpressed fin tip reaching two-thirds distance between pectoral-fin origin and pelvic-fin origin. Pelvic-fin with 1 unbranched and 8 (15) branched rays, second branched ray longest, adpressed fin tip not reaching base of anal-fin, axillary scale present at its base. Vent closer to anal-fin origin than to base of last pelvic-fin ray. Anal-fin with 2 (11) or 3 (4) unbranched and 5 (15) branched rays, first branched ray longest, adpressed fin tip almost reaching base of caudal fin. Caudal fin forked, lobe tips rounded, principal caudal rays 10+9 (15), tenth ray shortest, lobes more or less equal.

Lateral line complete, prominent, with 21 (11) or 22 (4) scales on the body; ½4/1/3½ scales in transverse line from dorsal-fin origin to pelvic-fin origin. Circumpeduncular scales 12 (15), predorsal scales 8 (14) or 9 (1), prepelvic scale rows 9 (4) or 10 (11); pre-pelvic and pre-anal region scaled. Gill rakers on the first gill arch 1 (1) or 2 (2) on epibranchial, 1 (3) at angle and 8 (2) or 9 (1) on ceratobranchial. Five infraorbital bones (IO1–5) ( Fig. 4 A); IO3 largest, deep, partly overlapping preoperculum; pharyngeal teeth 5, 3, 2 (3). Caudal-fin rays supported by neural and haemal spines of second and third preural caudal centra, single pleurostyle and epural, six hypural elements, one parhypural and free uroneural absent ( Fig. 4 B). Vertebrae (abdominal+caudal): 18+13 = 31 (2) or 18+14 = 32 (1); post-epiphysial fontanelle absent.

Coloration: In life: Dorsum and side golden yellow above lateral line, red below lateral line. Cheek, gill cover and region of cleithrum golden yellow with scattered red pigment. Snout grey. Lower parts of head white. A black humeral spot on scale row below the 3rd and 4th lateral-line scales and a prominent black caudal-peduncle blotch centered above the insertion of the last anal-fin ray, overlapping lateral line scales 16–18 or 17–19. Dorsal-fin hyaline, tinged golden yellow, with two rows of black bars on inter-radial membrane posterior to last unbranched ray. Pectoral-fin grey, pelvic- and anal-fins red, base of anal fin yellow. Caudal fin bright yellow.

In Alcohol: Coloration of freshly-preserved specimens similar to that of live specimens, fading with preservation. Dorsum light brown with darker scale pockets; sides becoming gradually lighter towards abdomen, which is white; cheek, and region of cleithrum silvery with sparse grey pigments; gill cover and iris white. Snout grey; ventral portion of head white. Dorsal-fin hyaline with two rows of black bars on inter-radial membrane. Pectoral, pelvic, anal and caudal fins hyaline without any markings. Humeral spot on scale row below the 3rd and 4th lateral-line scales. A prominent caudal-peduncle blotch centered above the insertion of the last anal-fin ray, overlapping lateral line scales 16–18 or 17–19.

Distribution. Presently known only from the Aivapui River and Keisalam River (Karnaphuli River drainage), a small stream inside Dampa Tiger Reserve, Mizoram, Northeast India ( Fig. 3 ). The Karnaphuli River, locally known as the Khawthlang Tuipui, in Mizoram, is located between the Ganges-Brahmaputra and the Kaladan drainages. Originating from the hills of the Mizoram-Tripura border in India, it flows along the Mizoram- Bangladesh border and then southwest through the Chittagong Hill tract and Chittagong and empties into the Bay of Bengal.

Etymology. The species name is an adjective, ‘rutila’ = reddish in Latin, referring to the reddish coloration of this fish.

Figures

FIGURE 2. Pethia rutila; A, holotype, ZSI FF 5215, 44.6 mm SL; B, paratype, PUCMF 14004, 40.2 mm SL, freshly preserved specimen; C, P. expletiforis, PUCMF 12006, 38.5 mm SL, freshly preserved specimen.

FIGURE 3. The collection locality of Pethia rutila (●). Circle may represent more than a single locality.

FIGURE 4. Pethia rutila. PUCMF 14006, 43.9 mm SL: A, infraorbital series; B, caudal skeleton. Abbreviations: CC, compound centrum; Ep, epural; H 1 – 6, hypurals 1 – 6; IO 1 – 5, infraorbitals 1 – 5; Ph, parhypural; Pls, pleurostyle; PU 2. preural centra 2; So, supraorbital. Scale bars = 1 mm.

Tables

TABLE 1. Biometric data for Pethia rutila (ZSI FF 5215; ZSI FF 5216; PUCMF 14004, 14005, 14006) (n = 15). Ratios are expressed as percentage of SL and HL. Ranges include value of holotype.

	holotype	mean	s.d.	range
Standard length	44.6			31.2–45.3
In % SL
Head length	27.4	27.1	0. 8	25.4–28.5
Snout length	7.6	7. 8	0.7	6.5–8.7
Eye diameter	7.8	8.4	0.7	7.3–9.5
Interorbital width	10.8	9.9	0.6	8.7–11.1
Head width	15.7	15.3	0.9	13.5–16.7
Head depth	21.1	21.9	0.9	20.6–23.2
Body depth	38.6	37.6	1.7	35.1–41.7
Predorsal length	52.9	52.9	1.5	50.1–54.9
Prepelvic length	48.4	49.0	1.3	46.9–51.9
Preanal length	71.5	70.8	1.6	66.6–72.4
Caudal-peduncle depth	14.3	14.3	0.7	13.3–15.9
Caudal-peduncle length	18.6	20.0	1.2	18.0–21.8
Dorsal-fin height	25.8	27.3	1.1	25.8–29.5
Anal-fin length	19.7	19.0	0.8	17.5–20.2
Pectoral-fin length	22.9	23.8	1.2	21.9–25.8
Pelvic-fin length	23.7	22.6	1.3	20.4–24.8
In % HL
Snout length	28	28	2.1	25–31
Eye diameter	29	31	2.4	28–35
Interorbital width	39	37	2.4	31–41
Head width	57	56	2.9	51–59
Head depth	77	81	2.6	76–85