ABORICHTHYS WAIKHOMI, A NEW SPECIES OF FISH (TELEOSTEI : NEMACHEILIDAE) FROM ARUNACHAL PRADESH, INDIA

The fishes of the genus Aborichthys Chaudhuri are smaliloaches generally found in torrential hill streams in the Darjeeling Himalayas, north eastern India and upper Myanmar. They are characterized in having elongated and compressed body; anus situated far forwards; pelvic fins extend considerably beyond the anal opening; dorsal fin inserted slightly behind pelvic fins; oblique narrow stripes on body; rounded caudal fin, which is usually marked with concentric black rings and a black spot at the upper corner of caudal base (Chaudhuri, 1913; Hora, 1925). While describing Aborichthys rossamai, Sen (2009) remarked that it is very much similar to genus Schistura McClelland and except for the forward position of the anus other characters of the genus are lacking in it. Menon (1987) considered Aborichthys as a subgenus of Noemacheilus van Hasselt. However, Talwar and Jhingran (1991), Jayaram (1999) and Viswanath et al. (2007) considered Aborichthys as valid genus. So far five species are described under the genus. They are A. kempi, A, elongatus, A. garoensis, A. tikaderi and A. rosammai. During field survey conducted by the Zoological Survey of India in the Namdapha National Park and Tiger Reserve, Arunachal Pradesh in 2009, six specimens of an undescribed Aborichthys were collected from the hill streams of Noa-Dihing river (Figs. 1-2). The species is herein described as Aborichthys waikhomi sp. nov. MATERIALS AND METHODS


INTRODUCTION
The fishes of the genus Aborichthys Chaudhuri are smaliloaches generally found in torrential hill streams in the Darjeeling Himalayas, north eastern India and upper Myanmar. They are characterized in having elongated and compressed body; anus situated far forwards; pelvic fins extend considerably beyond the anal opening; dorsal fin inserted slightly behind pelvic fins; oblique narrow stripes on body; rounded caudal fin, which is usually marked with concentric black rings and a black spot at the upper corner of caudal base (Chaudhuri, 1913;Hora, 1925). While describing Aborichthys rossamai, Sen (2009) remarked that it is very much similar to genus Schistura McClelland and except for the forward position of the anus other characters of the genus are lacking in it. Menon (1987) considered Aborichthys as a subgenus of Noemacheilus van Hasselt. However, Talwar and Jhingran (1991), Jayaram (1999) and Viswanath et al. (2007) considered Aborichthys as valid genus. So far five species are described under the genus. They are A. kempi, A, elongatus, A. garoensis, A. tikaderi and A. rosammai. During field survey conducted by the Zoological Survey of India in the Namdapha National Park and Tiger Reserve, Arunachal Pradesh in 2009, six specimens of an undescribed Aborichthys were collected from the hill streams of Noa-Dihing river (Figs. 1-2). The species is herein described as Aborichthys waikhomi sp. nov.

MATERIALS AND METHODS
The specimens were preserved in 10% formalin. Measurements and counts followed Jayaram (1999). Measurements were made to the nearest 0.1 mm on the left side of specimens whenever possible. The type specimens are deposited in the Zoological Survey of India at Estuarine Biology Regional Centre, Gopalpur-on-Sea and Arunachal Pradesh Regional Centre, Itanagar. Abbreviations used are: HL, Head length; EBRC/ZSI/F, Estuarine Biology Regional Centre/Zoological Survey of India/Fish; Max, Maximum; Min, Minimum; n, number of specimens examined; SD, Standard deviation; SL, Standard length; V / APRC/ ZSI/ P, Vertebrate/ Arunachal Pradesh Regional Centre/ Zoological Survey of India/Pisces. Diagnosis: A species of Aborichthys distinguished from its congeners by the combination of the following characters: 12-16 oblique black bands, narrower than interspaces at caudal peduncle; anus situated closer to caudal fin base than to tip of snout; dorsal fin insertion equidistant between snout tip and base of caudal fin; barbels much longer than eye diameter; incomplete lateral line terminating before pelvic fins; truncated caudal fin with irregular black blotches; a distinct black blotch on upper angle of caudal fin base.
Description : Morphometric data are given in Table 1. Body elongated and compressed. Head depressed, longer than caudal fin. Snout slightly rounded. Eye small, situated on dorsal side, not visible from ventral surface, its diameter smaller than interorbital space. Mouth inferior, semicircular; lips fleshy, upper lip continuous, lower interrupted in middle. Nostrils close to each other, closer to eye than tip of snout. Barbels three pairs; well developed, longer than eye diameter. Scale minute, embedded; lateral line incomplete, terminating before the origin of pelvic fin. Anus situated distinctly nearer to base of caudal fin than the snout tip. All fins greatly removed from one another. Dorsal fin small, with 2 simple and 7 branched rays, devoid of a spine, less than length of head; origin of dorsal fin equidistant between snout tip and caudal base. Pectoral with one simple and 9-10 branched rays, shorter than head. Pelvic fin with one simple and 6 branched ray, shorter than pectoral; its origin slightly in front of dorsal fin origin, extending considerably beyond anal opening. Anal fin base short, with 2 simple and five branched rays not reaching base of caudal, r Caudal fin with 15-16 branched rays, more or less truncated (Fig. Sf).
Colour: Body yellowish with 12 to 16 black oblique bands directed backwards from occiput to caudal base usually forked in front of dorsal fin, narrower than interspaces on caudal peduncle region. Upper surface and sides of head marked with irregular black blotches. Dorsal fin with 2 or 3 irregular series of spots; pectoral and pelvic fins with few black markings; anal dull white; caudal fin with irregular black blotches; upper extremity of caudal base marked with a distinct broad black spot. In life dorsal and caudal fins orange. Discussion: Aborichthys waikhomi is similar to A. elongatus and A. kempi in having vent situated distinctly nearer to caudal fin base than snout tip and a black blotch at upper end of base of caudal fin. However, it can be easily distinguished from the A. elongatus in having 12-16 oblique black bands on body from occiput to the caudal base alternating with broader interspaces in the caudal peduncle (vs. only posterior part of body marked with several broad bands, alternating with narrower interspaces), truncated caudal fin with irregular black blotches (vs. rounded with 2 short whitish bands in the middle), incomplete lateral line (vs. complete), barbels longer than eye diameter (vs. more or less equal), longer pectoral fins and more forward position of anus (Table 2). It is distinguished from A. kempi in having truncated caudal fin with irregular black blotches (vs. rounded with two broad black concentric curves), 12-16 oblique bands on body (vs. 18 to 21), more distinct bands on posterior-third of body (vs. indistinct), longer head; anus more nearer to caudal fin base than snout and more posteriorly placed pelvic and anal fins ( Table 2). The new species is similar with A. rosammai in having a truncated caudal fin and anus situated distinctly nearer to caudal fin base than snout tip. However, it differs from the latter in having irregulars black blotches on caudal fin (vs. dull white), 12-16 black bands on body (vs. lO (Table 2). A. waikhomi can be easily distinguished from A. garoensis and A. tikaderi in having anus situated distinctly nearer to caudal fin base than snout tip (vs. nearer to snout tip), dorsal fin origin equidistant between snout tip and caudal fin base (vs. nearer to snout tip) and truncate caudal fin (vs. rounded).

Distribution: Presently known from streams of
All the known species of Aborichthys are endemic in theBrahmaputra drainage except A. kempi which was reported from the Putao plains in upper Myanmar. Chaudhuri (1919) and Hora (1925) remarked that the Burmese specimens of A. kempi differ considerably from the Assamese regarding colouration and proportions, but the material available did not justify their specific separation. Kottelat (1990) suggested that new collections, or at least access to the existing collection, would be greatly desirable for solving the problem of specific identity of the Burmese specimens. The uplift of the Indo-Burman mountain range not only separated the Upper Brahmaputra from the Ayeyarwaddy of Myanmar led to the formation of a large number of mountains and hill streams, each of which evolved its own fish fauna (Vishwanath et al. 2010). The fishes of Aborichthys seem to be in the process of adaptation in the torrential hill streams of these two drainages. Menon (1987) remarked that the gradual shifting of vent forward provides the fish with a longer tail for life in swift current. Hora (1925) opined that A. garoensis is a highly specialized form and throw a great deal of light on the evolution of the genus. However, the present status of these fishes and their distribution in Myanmar is yet to be studied. A detail survey and phylogenetic study of the species of Aborichthys in both the drainage systems would be of great interest.

SUMMARY
A new freshwater fish Aborichthys waikhomi is described here from the streams of Noa-Dihing river, Brahmaputra basin in Arunachal Pradesh, India. It is distinguished from all other known species of Aborichthys in having truncate caudal fin with irregular black blotches and 12-16 oblique black bands on body, which are narrower than Rec. zool. Surv. India interspaces in caudal peduncle. The fishes of Aborichthys seem to be in the process of adaptation in the torrential hill streams. A detail survey on the fish fauna of the Brahmaputra and the Ayeyarwaddy drainages may provide better understanding on the status and zoogeographical distributions of these fishes.

ACKNO~EDGEMENTS
I am grateful to Dr. K Venkataraman, Director, Zoological Survey of India, Kolkata for encouraging and permitting me to examine the type specimens of Aborichthys. I am also thankful to Dr. KC. Gopi, Scientist 'E Dr. AK Karmakar, Scientist, B. ReId. and Shri A Das of Freshwater Fish Section, ZSI for their helps and co-operations during the study in the section. I would like to thank Dr. G. Maheswaran, Officer-in-Charge, APRC, ZSI, Itanagar for proving registration number of type specimens and Smt. Tapasini Batracharjee, Librarian, ZSI, Kolkata for providing literatures.