DESCRIPTION OF A NEW SPECIES OF ABORICHTHYS, CHAUDHURI FROM NORTH-EAST INDIA (PISCES: CYPRINIFORMES : BALITORIDAE)

A new species Aborichthys rosammai is described from North-East India. Other known species under the genus are kempi, elongatus, garoensis and tikaderi. The new species has been compared with all the known species to confirm for its separate identity. The genus is so far restricted to North East India with only A. kempi having its distribution in Myanmar also.


INTRODUCTION
The genus Aborichthys was first established by Chaudhuri (1913) with A. kempi as the type species.Subsequently, three other species namely A.elongatus (Hora, 1921), A.garoensis (Hora, 1925) and A.tikaderi (Barman, 1984) were described.All the species of Aborichthys are restricted so far within North East India with A.kempi having its distribution in Myanmar also.Jayaram (1999)  Diagnostic characters of Schistura : Body elongate, compressed posteriorly; vent situated nearer anal fin; head either depressed or compressed; snout usually blunt; dorsal fin short, inserted ahead or opposite pelvic fin; pelvic fin never crosses anal opening; caudal fin slightly emarginate, forked or truncate, never rounded; lateral line incomplete or complete.
The present specimen does not tally with other known species of the genus Aborichthys and hence it is described here as new species, A. rosammai.The distinct and prominent characters exhibited by these specimens motivated the author to describe it new to science.The specimens are preserved in 5% formaldehyde.Morphological measurements were done with a slide caliper.Twenty two morphological characters have been taken into consideration for all the known species.Morphological data for 4 species namely, kempi, e[ongatus, garoensis and tikaderi have been taken from description of type species and comparative chart has also been incorporated (measurements converted into percentage from the original data).Measurements are expressed in percentage in relation to standard length.The mean value are shown in parenthesis (Table 2).
Measurements of different morphological characters of Holotype and Paratypes are shown in Table 1.Body somewhat cylindrical, it's depth 5.00-6.64times in standard length.Dorsal and ventral profile of the body is almost parallel.Head slightly depressed, it's depth 7.50-10.00,breadth 5.00-6.66,length 3.75-5.00times in standard length.Eyes large, placed slightly nearer to snout, dorsolateral in position; it's diameter 4.00-5.00times in head length.Snout rounded, 2.40-2.50times in head length.Nostrils placed almost midway between eye and tip of snout, with short barbel like projection.Mouth slightly behind tip of snout, lower lip interrupted in middle.Barbels 3 pairs, all of equal length, longer than eye diameter.Length of dorsal fin 5.3S-S.00,pectoral fin 5.00-6.66,pelvic fin 5.00-S.00,anal fin 6.00-7.50 and caudal fin 4.57-6.00times in standard length.Predorsal distance 1.S4-2.00,prepectoral distance 3.75-4.30,prepelvic distance 1.66-1.95and preanal distance 1.26-1.36times in standard length.Vent situated far forward towards pelvic fin, distinctly nearer base of caudal fin than tip of snout.The distance between snout to vent 1.60-1.72 and vent to base of caudal fin 2.40-2.71times in standard length.Length of caudal peduncle 5.3S-7.50 and height of caudal peduncle 7.50-10.00times in standard length.Lateral line complete.The dorsal fin placed slightly behind or opposite to pelvic fins, its origin slightly nearer to base of caudal fin than to tip of snout.Longest ray of dorsal almost equal to body depth immediately below it.Anal fin nearer to base of caudal fin than to commencement of pelvic fins.Length of pectoral fins slightly shorter than head length (1.17-1.33 times).The distance between origin of pectoral and pelvic fins (3.42-4.00times in standard length) shorter than the distance between pelvic and anal fins (3.59-5.00times in standard length).Caudal fin more or less truncate; slightly rounded near edge (Plate II, C; Fig. 1B); its length slightly shorter than the head length.Caudal peduncle short, 1.00-1.50times as long as high.

Aborichthys rosammai
Colour: Dorsal surface of head greyish, body with 10-11 bands.In caudal peduncle region bands coalesced.A dark band at the base of caudal fin (Fig. 1 B).All the fins are dull white.

DISCUSSION
To quote Hora (1925), "there is no doubt that fishes of the genus Aborichthys are evolved from those of the genus Nemachilus chiefly by the change in the position of the vent".This is very much true for the present species.Except for the position of vent the present species is morphologically very much similar to genus Schistura.The diagnostic characters of Aborichthys such as 'greatly elongated body, all fins greatly removed from one another, lunate caudal fin, a black spot at upper end of base of caudal fin' -all these characters are lacking in the present species.
Out of the 22 morphological characters ( shown in Table -2), the present specimens are showing differences in at least 12 -14 characters with other known species.
classified 12 genera under subfamily Nemacheilinae from Indian region, namely, Aborichthys, Acanthocobitis, Neonemacheilus, Nemacheilus, Schistura, Mesonemacheilus, Physoschistura, Longischistura, Oreonectes, Triplophysa, Nemachilichthys and Yunnanilus.Of these Aborichthys, Acanthocobitis, Nemacheilus, Mesonemacheilus, Schistura and Neonemacheilus are represented in North East India.While studying the fish collections from Subansiri river, Dhemaji district, Assam, the author came across a single specimen (26.25 mm TL) which at a glance looked like the genus Schistura but on detailed study the forward position of vent (Plate I,B,C; Fig. lA) revealed its identity as genus Aborichthys.Subsequently, another 4 examples (19 -28 mm TL) were collected from Sippi river, Daporijo, Subansiri district, Arunachal Pradesh.Diagnostic characters of Aborichthys : Body greatly elongated and compressed; vent situated far forwards; nostrils openings with barbel-like outgrowths; head flattened slightly, anterioly rounded; snout conical and broadly rounded; dorsal fin inserted slightly behind pelvic fins; pelvic fins extend beyond anal opening; all fins greatly removed from one another; caudal fin lunate; lateral line incomplete, indistinct.