Mystus ngasep, a new catfish species (Teleostei: Bagridae) from the headwaters of Chindwin drainage in Manipur, India

Mystus ngasep, a new species of bagrid catfish from the headwaters of Chindwin drainage in Manipur, India, is described here. It is distinguished from its congeners in having a unique combination of the following characters: a colour pattern of the body consisting of a distinct dark tympanic spot and three brown stripes separated by pale narrow longitudinal lines, cranial fontanel reaching the base of the occipital process, a long-based adipose fin contacting the base of the last dorsal-fin ray anteriorly, 16-19 gill rakers on the first branchial arch, a slender cleithral process, pectoral spine with 9-11 serrations on the posterior edge, eye with a diameter of 16.5–19.8 % HL and prepectoral length 22.2–26.0 % SL. The new species has been compared with its congeners from Myanmar and also from northeastern India.


IntroductIon
Fishes of the genus Mystus Scopoli are small to medium-sized bagrid catfishes occurring in South Asia.Roberts (1994) recognized Mystus to have an elongate cranial fontanel reaching up to the base of the occipital process, long maxillary barbel, very long adipose fin, 11-30 gill rakers on the first gill arch and 37-46 total vertebrae, about equally divided between abdominal and caudal regions.He included only eight species under the genus.Mo (1991) characterized the genus to have a thin needle-like first infraorbital, twisted and thickened metapterygoid loosely attached to the quadrate by means of ligament or a small extent of cartilage.Jayaram & Sanyal (2003) and Ferraris (2007) respectively listed 44 and 33 species of Mystus as valid.
Manipur State in the northeastern corner of India has two headwaters: that of the Brahmaputra basin in the west and of the Chindwin in the east.Hora (1921) reported Mystus bleekeri from the lakes and streams of Manipur Valley, including the Loktak Lake (all headwaters of the Chindwin River drainage).Hora (1936) also collected the species from the Brahmaputra basin in Nagaland and Menon (1954) from Manipur.The species was also reported from the Chindwin basin of Manipur by Menon (1953Menon ( , 1954)), Singh & Singh (1985), Vishwanath et al. (1998), Arunkumar & Singh (1997) and Vishwanath (2000).
Present studies reveal that the species of Mystus occurring abundantly in the streams, rivers and lakes (all belonging to the Chindwin drainage) in the valley of Manipur are without a name and the species has been misidentified as M. bleekeri after Hora (1921).The species is herein described as Mystus ngasep sp.nov.

MaterIal and Methods
Materials examined are deposited in the Manipur University Museum of Fishes (MUMF).Measurements were made with a dial caliper to the nearest 0.1mm.Body proportions were expressed in percentage of SL and HL.Counts and measurements follow those of Ng & Dodson (1999).Dorsal fin height was measured from the base of the spinelet to the highest point of the dorsal fin.For osteological studies, clearing and staining techniques follow Hollister (1934).Methods for counting gill rakers and vertebrae follow Roberts (1992) and Roberts (1994), respectively.
Mystus bleekeri Menon, 1953: 266 (listed from Manipur valley); Menon, 1954: 22 (in  diagnosis Mystus ngasep sp.nov.can be distinguished from congeners in having a unique combination of the following characters: a colour pattern consisting of a distinct dark tympanic spot and three brown stripes separated by pale narrow longitudinal lines on the sides of the body, cranial fontanel reaching the base of the occipital process, a long-based adipose fin contacting the base of the last dorsal-fin ray anteriorly, 16-19 gill rakers on the first branchial arch, a slender cleithral process (Fig. 1), pectoral spine with 9-11 serrations on the posterior edge, eye small with its diameter 16.5-19.8% HL, pectoral and anal fins with 9-10 and 8-9 branched rays respectively and short maxillary barbel (200.0-235.0% HL).

description
Morphometric data are shown in Table 1.Dorsal profile rising evenly (at an angle of 20-25 0 to the horizontal) from tip of snout to origin of dorsal fin then goes almost horizontal to anterior third of adipose fin, then sloping gradually ventrally from there to end of caudal peduncle.Ventral profile roughly straight to end of anal-fin base, then sloping gently dorsally to the end of caudal peduncle.
Head depressed.Skin covering on dorsal surface of head thin.Anterior cranial fontanel extending from level of posterior nasal opening to posterior orbital margins, separated from posterior fontanel by epiphyseal bar.Posterior fontanel extends to the base of the supraoccipital process.Supraoccipital process long, reaching basal bone of dorsal fin, its base narrow with about one-fifth of its length, distally tapered.Eye ovoid, horizontal axis longest, located entirely in the dorsal half of the head.
Mouth sub-terminal.Oral teeth small and villiform, arranged in irregular rows.Premaxillary tooth band slightly curved backward, of equal width throughout.Tooth band on vomer continuous across midline and crescentic, slightly broader than premaxillary in middle, tapering posterolaterally, extending to level of lateral end of premaxillary tooth band.Dentary tooth band separated in the middle by thick skin, tapering laterally on each side, broader than premaxillary and vomerine tooth band at symphysis, length of one side equals lateral span of vomerine tooth band.Gill openings wide, free from isthmus.First branchial arch has 16-19 gill rakers.
Barbels in four pairs, maxillary barbel not reaching anal-fin origin, nasal reaching posterior rim of eye, outer mandibular barbel reaching base of pectoral fin and inner mandibular barbel slightly shorter.Skin smooth.Lateral line complete and midlateral in position.Dorsal-fin origin slightly anterior to the middle of the body, with spinelet, spine, and seven branched rays.Dorsal spine three-fifths to three-fourths of dorsal-fin height, smooth on both edges.Adipose fin long, spanning most of postdorsal distance, its origin in contact with base of last dorsal-fin ray and deeply incised posterior portion.Pectoral fin with I, 9-10 rays, fin margin straight posteriorly.Pectoral spine backwardly curved with 9-11 large posterior serrations and anteriorly rough.Pelvic fin short with i,5 rays.Anal-fin origin inserted at vertical through middle of adipose-fin base, with iii-v, 8-9 rays, anterior two simple rays minute, visible in alizarin stained specimens.Caudal fin deeply forked with i,7,8,i rays, upper lobe longer.
sexual dimorphism: Males with long genital papilla reaching to the base of the second branched anal-fin ray.Females with rounded genital opening.
colour: In life or freshly dead: dorsal portion of the head and body brownish-grey with greenish reflection; tympanic spot without distinct margin, with greenish reflection that is more pronounced in the middle; lateral surface of body silvery with brownishgolden reflection without prominent stripes, ventrally dull white.
In 10% formalin: dorsal portion of the head and body brownish-gray, tympanic spot with distinct margin, three brown lateral stripes on body separated by pale longitudinal lines, lower pale longitudinal line about twice as wide as the upper.Caudal-fin base without dark spot.

etymology
The specific epithet is derived from the Manipuri local name of the fish: 'Ngasep'.

distribution
Presently known from the Loktak Lake, Nambul, Manipur, Iril, Imphal, Khuga rivers and the tributaries of the Yu river (all belonging to the Chindwin River drainage) in Manipur.dIscussIon Ng & Kottelat (2009) clarified the identity of Mystus bleekeri and restricted its distribution to the Ganga-Brahmaputra basin while M. rufescens was found to be limited to the Irrawaddy basin.Their conclusion was based on the very distant geographical origins of the type series of M. bleekeri (Sind, Yamuna, upper waters of Ganga and Burma) which predicted involvement of more than one species; Day's (1877) observation of a black spot at the base of the caudal fin in the Burmese specimens and Roberts's (1994) reference of Day's type material from Burma as M. rufescens.
As mentioned earlier, six congeners of Mystus ngasep sp.nov.are known from Myanmar.Among those, M. cineraceus, M. rufescens and M. falcarius are very similar to the new species in having a long-based adipose fin that contacts the base of the last dorsal-fin ray anteriorly and cranial fontanel reaching to the base of the occipital process.A diagnostic summary of the species of Mystus from the Chindwin-Irrawaddy and Ganga-Brahmaputra River drainages is given in Table 2.
The new species differs from Mystus cineraceus in having three brown stripes on the body separated by pale narrow longitudinal lines above and below the lateral line (vs.a brownish body with a midlateral stripe lacking the pale longitudinal lines).It further differs from M. cineraceus in having more gill rakers on the first branchial arch (16-19 vs. 13-15; Table 3), more pectoral-fin rays (9-10 vs. 7-8), more analfin rays (8-9 vs. 6-7) and a shorter maxillary barbel .
Specimens of Mystus rufescens collected from the Chindwin basin in the Indo-Burma border in Manipur were examined and found to have a long-based adipose fin contacting the base of the last dorsal-fin ray anteriorly, a cranial fontanel reaching the base of the occipital process and a black spot at the base of the caudal fin.Vinciguerra's (1890) description of the species clearly states the presence of a black spot at the base of the caudal fin.We have also examined a syntype of M. bleekeri , labelled as ZSI 781, collected from Prome (=Pyay), Myanmar.The ZSI specimen has all the diagnostic characters of M. rufescens and also bears a noticeably darker region at the base of the caudal fin.The new species can be easily differentiated from M. rufescens by the absence of a black or dark brown spot at the base of the caudal fin (vs.spot present; Image 2), shorter maxillary barbel 2) and smaller eye .
Mystus ngasep sp.nov.differs from M. falcarius and M. cavasius in having (vs.lacking) brown lateral stripes on the body, a shorter maxillary barbel (200.0-235.0% HL vs. 355.8-538.0), a lower dorsal fin ) and lacking the black spot in front of dorsal spine (vs.spot present).
Mystus ngasep sp.nov.differs from M. leucophasis and M. pulcher in having a longer cranial fontanel reaching the base of the occipital process (vs.not reaching, but extending up to half the length of supraoccipital bone); adipose-fin base in contact (vs.not in contact) with the base of the last dorsalfin ray anteriorly, and a smooth (vs.serrated) dorsal spine.Mystus leucophasis further differs from the new species in having (vs.lacking) a filamentous extension of the upper principle-ray of the caudal fin.M. ngasep sp.nov.further differs from M. pulcher in having a wider vomerine tooth-band (as wide as the premaxillary tooth-band vs. about one-third of the premaxillary tooth-band), fewer vertebrae (41-42 vs. 35) and lacking (vs.having) a black spot at the base of the caudal fin.
Mystus ngasep sp.nov.differs from M. carcio in having more vertebrae (40-41 vs. 32), a longer adiposefin base (37.), vomerine tooth-band continuous (vs.interrupted in the middle), fewer gill rakers on the first arch (16-19 vs. 23-24) and lacking (vs.having) the coracoid shield below the pectoral fin.It differs from M. gulio in having a longer occipital process (reaching to the basal bone of dorsal fin vs. not reaching), origin of adipose-fin base in contact (vs.not in contact) with the base of the last dorsal-fin ray, and a smooth (vs.posteriorly serrated) dorsal spine.
20.2-25.9),shorter maxillary barbel (200.0-235.0% HL vs. 241.3-330.0),more gill rakers on the first branchial arch(16-19 vs. 11-15), fewer pectoral spine serrations on the posterior edge(9-11 vs. 11-16)  and longer prepectoral length) and dorsal spine that extends to about three-fifths to three-quarters (vs.nearly half) of the fin height.It further differs from M. bleekeri in having a narrower base of the supraoccipital process, its width at the base being about one-fifth of its length (vs.two-fifths to half of its length); more vertebrae (40-41 vs. 37-40), with the closure of the haemal arches appearing from the 12 th -14 th (vs.commonly 11 th or rarely 12 th ) vertebra onwards.Mystus ngasep differs from M. dibrugarensis in having fewer gill rakers (16-19 vs. 28) on the first arch, more vertebrae (40-41 vs. 36), the absence (vs.presence) of a thin black mid-lateral line connecting the tympanic spot and the black spot at the base of the caudal fin.It differs from M. tengara in having a smooth (vs.with 8-9 serrations posteriorly) dorsal Image 2. Mystus rufescens (MUMF 9530) 101.1mmSL.

Table 3 . Frequencies of gill rakers count in four species of Mystus with a long adipose fin distributed in the Chindwin- Irrawaddy River drainage. Total numbers of gill rakers on the first branchial arch
M. armatus, because M. armatus also possess a black spot at the base of the caudal fin also present in M. rufescens.We have also not encountered any species of Mystus with a black spot at the base of the caudal fin from our extensive surveys of the Brahmaputra River drainage in Manipur.However, we were unable to verify the identity ofJayaram & Sanyal's (2003) material, as we were unable to locate this material for study in the collections of the Zoological Survey of India in Kolkata.Jayaram & Sanyal (2003) also misidentified several specimens collected from the Chindwin River drainage in Manipur (ZSI 4236/2, ZSI F 4293/2, ZSI F 4346/2) as M. bleekeri.Mystus ngasep sp.nov. is very similar in colouration and meristic counts to M. bleekeri.However, the new species differs from M. bleekeri in having a slender (vs.broad) cleithral process, smaller eye (diameter 16.2-19.8% HL vs.