122 Records of the Indian MuseuDi. [Vol, III, 



The record^ of fish obtained from the northern area are, of 

 course, still somewhat scanty. They are to be found in the Fauna 

 of British India (comprising fish from Leh and Ladak), Tate 

 Regan's reports on the fish collected during the Tibet mission, and 

 Ivloyd's report in the present series. 



From the northern area seventeen species of fish are at present 

 known, belonging to the families Siluridse and Cyprinidae.^ From 

 the southern area thirty-six species of these two families are recor- 

 ded in the Fauna of British India. These two groups have onl}- 

 two species in common {Schizothorax esocinus and Diptychus macu- 

 latus). (These two species are also the only forms from the 

 Trans-Himalayan Indus which have not hitherto been found in the 

 Trans-Himalayan Brahmaputra. Thus there are no species common 

 to the latter and to the rivers of the south face of the Himalayas.) 

 Thus of these two families there are fifteen species confined to the 

 northern region, thirt3^-four to the southern, and two are found in 

 both. 



The separation of the two groups may be chiefl}^ due to (i) a 

 physical obstacle separating the two water-systems and preventing 

 the passage of fish from one system to another, or (2) some differ- 

 ence in the biological environment in the two systems. 



(i) It would appear that the importance of a watershed as a 

 barrier might be very, easily exaggerated. The Tang-la is the 

 watershed between the Nyang-.chu, which runs into the Brahma- 

 putra, and the Amu-chu, which runs into the Raidak. With a 

 height of 15,200 feet it might be expected to form a fairly efficient 

 obstacle. We find, however, that the streams on the two sides of 

 the pass are separated by a distance of at the most one mile, and 

 that this mile consists, not of abrupt cliffs, but of gently sloping 

 open ground. In the rainy season the smallest rivulets doubtless 

 approach each other much more closely. To the north of the 

 Tang-la a series of rivulets and marshes extends throughout the 

 twenty miles which separate the pass from the Rham-Tso. Such 

 a watershed is not likely to prove a more efficient barrier in its 

 purely physical aspect, than, for instance, the watershed separat- 

 ing the Clyde and the Tweed. 



In this connection it may be noticed that the young of these 

 river fish are extremely fond of intruding themselves into the 

 smallest and shallowest streams. 



(2) With no further data than those at present at our disposal, 

 it is not possible to discuss differences in biological surroundings 



1 Salmonidse are not known from the basins of either the Indus or Brahma- 

 putra. In the collection.s of the Indian Museum are specimens of a Sahno which 

 have been identified by Tate Regan as S. oxianns, Kessler. Tate Regan considers 

 this species to be only doubtfully distinct from S fario, the common British brook 

 trout. These specimens come from ( i ) the Koksha river, Zila, Chitral. at a height 

 of 8,000 feet above sea-level, and (2) from small tributaries of the Bammian river 

 in Northern Afghanistan at a height of 10,000 feet. Both the Koksha and Bam- 

 mian rivers run northward into the Oxus. 



These are the two points at which the Salmonidte approach most closely to 

 the rivers of the Himalayas. 



