Mystus prabini, a new species of catfish (Siluriformes: Bagridae) from Arunachal Pradesh, north-eastern, India Author Darshan, Achom Author Abujam, Santoshkumar Author Kumar, Ram Author Parhi, Janmejay Author Singh, Yambem Suresh Author Vishwanath, Waikhom Author Das, Debangshu Narayan Author Pandey, Pramod Kumar text Zootaxa 2019 2019-07-31 4648 3 511 522 journal article 25832 10.11646/zootaxa.4648.3.6 b73ebab8-3acc-4900-b261-bbf713145f24 1175-5326 3356404 F4D1CCCA-35C2-4CFA-984D-7A5D91769311 Mystus prabini , sp. nov. ( Fig. 1 ). Holotype : RGUMF 499 , 82.2 mm SL; India , Arunachal Pradesh , Lower Dibang district , Sinkin River (a tributary of the Siang River ) at Anpum village , 28°0′4.4″N & 95°35′9.6″E , Achom Darshan , Santoshkumar Abujam , and Ram Kumar , 3 February 2015 . Paratypes : RGUMF 308-315 , 8 ex. , 70.8–113 mm SL, same data as holotype . RGUMF—MN2 - MN 5; 4 ex. 72.3–95.5 mm SL, same data as holotype. RGUMF-316, 6 ex. , 62.3–87.9 mm SL; ZSI / APRC P-1660 , 2 ex. , 70.1– 82.7 mm SL, India , Arunachal Pradesh , Lower Dibang Valley district , Dibang River at Bomjir village , 28°9′17.5″N & 95°40′13.6″E , Achom Darshan and Santoshkumar Abujam , 5–7 February 2016 . Diagnosis. Mystus prabini differs from all South-Asian congeners except M. bleekeri (Day) , M. cavasius (Hamilton) , M . zeylanicus Ng & Pethiyagoda , M. falcarius Chakrabarty & Ng , M. seengtee (Sykes) , M. cineraceus Ng & Kottelat , M. ngasep Darshan et al. , M. rufescens (Vinciguerra) , and M. ankutta Pethiyagoda et al . in having a long adipose-fin base that reaches anteriorly (vs. a short adipose fin that does not reach) the base of the last dorsal-fin ray. The new species is distinguished from the nine named species in having (vs. lacking) a narrow blackish mid-lateral stripe extending from the anterior region of the tympanic spot to the rounded spot at the caudal-fin base ( Fig. 2 ). Further, the new species differs from all congeners by the combination of the following characters: posterior cranialfontanel reaching the base of the occipital process, predorsal length 34.7–41.0% SL, pre-anal length 66.9–74.2% SL, pre-pelvic length 46.8–52.0% SL, pre-pectoral length 17.2–25.8% SL, caudal peduncle depth 9.8–12.1% SL, body depth at anus 17.1– 25.1% SL, head length 22.0–25.6% SL, snout length 34.1–38.6% HL, eye diameter 20.1–25.0% HL, and interorbital distance 33.1–41.0% HL. FIGURE 1. Lateral view of Mystus prabini sp. nov. , RGUMF 499, 82.2 mm SL, holotype, the Sinkin River at Lower Dibang valley district, Arunachal Pradesh. Description . Morphometric data are presented in Table 2 . Head depressed. Skin covering on dorsal surface of head thin. Anterior cranial-fontanel extending from level of posterior naris to posterior orbital margin, separated from posterior cranial-fontanel by epiphyseal bar. Posterior cranial-fontanel extending to base of supraoccipital process. Supraoccipital process long, gently tapering caudad to basal bone of dorsal fin, width of its base about one-fifth its length. Eye ovoid, horizontal axis longest, located entirely in dorsal half of head. Mouth sub-terminal. Oral teeth small, villiform, arranged in irregular rows. Premaxillary tooth band slightly curved backward, of equal width throughout. Tooth band on vomer continuous, crescentic, about twice as broad as premaxillary tooth band, tapering posterolaterally, its lateral span slightly wider than that of premaxillary tooth band. Dentary tooth band separated medially by dermal ridge, tapering laterally on each side. Gill openings wide, free from isthmus, gill rakers 2+8=10 (6) or 2+9=11 (3) or 3+9 =12 (1) or on first branchial arch. Vertebrae 21+18= 39 (2) or 22+17=39 (2) or 22+ 18=40 (1); 8 (5) branchiostegal rays; caudal-fin skeleton with 5 hypural plates, first and second support lower lobe, and third, fourth and fifth support upper lobe. TABLE 2. Morphometric measurement of Mystus prabini sp. nov. (N=21) and Mystus dibrugarensis (N=16).

Mystus prabini sp. nov.		Mystus dibrugarensis
Holotype	Range	Mean±SD	Range	Mean±SD
RGUMF 499
Total length in mm	104	76.9–140	67.2–101
Standard Length in mm	82.2	62.3–113	53.3–66.2
In % Standard Length
Predorsal length	37.9	34.7–41.0	38.0±2.04	34.6–40.8	37.4 ± 1.63
Preanal length	70.6	66.9–74.2	70.3±2.13	62.8–72.5	68.8 ± 2.45
Prepelvic length	49.2	46.8–52.0	48.8±1.53	46.6–53.5	50.9 ± 1.74
Prepectoral length	23.3	17.2–25.8	22.2±2.16	19.2–25.4	22.7 ± 1.38
Height of dorsal fin	15.4	15.4–20.1	17.7±1.64	16.1–21.1	19.2 ± 1.61
Length of dorsal-fin base	14.1	9.9–14.1	11.8±1.13	12.1–15.1	14.0 ± 0.76
Dorsal-spine length	11.9	9.8–12.7	11.3±0.84	9.0–13.4	11.8 ± 1.34
Anal-fin length	15.1	10.5–15.2	13.0±1.29	13.1–18.4	14.9 ± 1.35
Pelvic-fin length	13.2	12.0–15.5	14.1±1.17	12.2–17.6	14.7 ± 1.21
Pectoral-fin length	15.7	13.6–18.5	16.3±1.37	13.9–20.0	17.7 ± 1.43
Pectoral-spine length	14.3	12.8–16.2	14.5±0.86	15.3–19.6	13.4 ± 7.41
Caudal-fin upper lobe length	26.7	21.5–29.7	25.6±2.24	24.2–30.8	27.3 ± 1.98
Caudal-fin lower lobe length	21.6	18.7–24.0	19.4±5.42	21.5–27.6	24.0 ± 1.94
Length of adipose-fin base	45.1	38.1–45.1	42.6±2.33	16.1– 22.9	18.5 ± 2.22
Adipose maximum height	6.3	5.0–8.0	6.0±0.75	3.9–6.7	5.2 ± 0.67
Post-adipose distance	5.1	4.7–7.0	5.9±0.67	11.0–18.5	15.2 ± 2.14
Caudal-peduncle length	17.5	10.3–21.2	16.6±3.5	9.4–12.8	10.7 ± 1.2
Caudal-peduncle depth	11.1	9.8–12.1	10.8±0.67	12.3–13.7	16.5 ± 1.75
Body depth at anus	21.5	17.1–25.1	20.0±2.33	12.3–13.7	12.9 ± 0.44
Head length	22.7	22.0–25.6	23.8±1.02	20.6–24.8	22.6 ± 1.23
Head width	18.2	15.7–20.1	17.7±1.2	22.2–25.8	24.1 ± 1.00
Head depth	15.2	12.5–16.3	14.2±0.95	17.7–19.8	18.9 ± 0.56
In % Head length
Snout length	38.3	34.1–38.6	36.8±1.09	30.1–43.6	34.2 ± 3.36
Eye diameter	24.8	20.1–25.0	22.1±1.34	20.2–26.9	24.1 ± 1.74
Interorbital distance	40.6	33.1–41.0	36.3±2.09	39.5–50.5	43.6 ±3.28
Nasal-barbel length	50.5	39.5–58.9	47.3±5.6	50.9–82.9	66.6 ± 8.14
Maxillary-barbel length	265.0	228–293	254.1±19.19	265–345	305.6 ± 25.65
Inner mandibular-barbel L	72.1	52.4–82.2	66.1±8.59	79.4–107	92.9 ± 8.80
Outer mandibular-barbel L	115.2	83.6–131	109.0±11.18	130–161	150.4 ± 13.93

Barbels in four pairs: maxillary barbel terminating slightly ahead of anal-fin origin, nasal barbel crossing posterior rim of eye but not reaching base of supraoccipital process, outer mandibular barbel reaching to base of pectoral fin, inner mandibular barbel slightly shorter than outer. Skin smooth. Lateral line complete, midlateral in position. Dorsal-fin origin slightly anterior to middle of body, with I,7 rays. Dorsal spine length three-fifths to threefourths of dorsal-fin height, smooth on both anterior and posterior edges. Adipose fin long, spanning most of postdorsal distance, commencing at base of last dorsal-fin ray, terminating above middle of caudal peduncle, deeply incised posteriorly. Pectoral fin with I, 8–9 rays, spine slightly recurved with 11–15 large serrae on posterior edge, 26–43 minute serrations on anterior edge. Pelvic fin short, with i,5 rays. Anal-fin origin at vertical through middle of adipose fin, with iii, 8–9 rays, anterior first simple ray minute, visible only in alizarin stained specimens. Caudal fin deeply forked with i,7,8,i rays, its upper lobe longer than lower lobe. Colouration. In life, dorsal surface of body uniform dark brown, flank with narrow blackish mid-lateral stripe running above lateral line, extending from anterior region of blackish tympanic spot to rounded spot at caudal-fin base; greenish reflection appearing from dorsal and ventral margins of midlateral stripe, more distinct below region of dorsal fin; two broad pale-brown inter-stripes above and below midlateral stripe. Ventral surfaces of head and body dirty white, adipose fin dark brown. All fins hyaline; dorsal half of barbels brownish at base, dirty white dis- tally and ventrally. FIGURE 2. Lateral views of three species of Mystus showing the extent of adipose fin and the midlateral stripe: a. Mystus prabini sp. nov. , RGUMF 316, 87.9 mm SL, paratype; b. Mystus bleekeri , MUMF 9521, 89.2 mm SL; c. Mystus dibrugarensis , RGUMF 307, 65.5 mm SL. Etymology. The species is named for the late Prabin Kumar Mahanta, for his substantial contribution to the development of the cold-water fisheries sector in the Himalayan regions of India . Distribution. The new species is presently known from its type locality, the Sinkin river at Anpum village in Lower Dibang valley District, Arunachal Pradesh , and also from the Dibang River in Arunachal Pradesh , India ( Figs. 3–4 ).