STRUCTURAL MODIFICATIONS IN THE FISH OF 

 MOUNTAIN TORRENTS. 



By Sunder L,al Hora, M.Sc, Assistant Superintendent, 

 Zoological Survey of India. 



Contents. 



Page 



Introduction ... ... ... ... ... ... 31 



Conditions affecting fish in rapid waters ... ... ... 34 



Modifications for life in hilt-streams ... ... ... ... 35 



The external form ... ... ... ... ... 35 



The scale-covering, etc. ... ... ... ... 36 



The paired fins and the skeletal and muscular structures connected 



therewith ... ... ... ... ... ... 36 



The caudal fin and its peduncle ... ... ... ... 40 



The mouth, its position and shape ; the jaws ; the barbels ; the lips 



and their muscles ... ... ... ... ... 41 



The eyes ... ... ... ... ... ... 42 



The gill-opening, branchiostegal rays and membranes ... ... 43 



The air-bladder ... ... ... ... ... 43 



Special modifications of the skin ... ... ... ... 44 



The minute structure of the adhesive apparatus ... ... ... 47 



Cyprinoidea ... ... ... ... ... 47 



Siluroidea ... ... ... ... ... ... 51 



Conclusion ... ... ... . ... ... ... 58 



Origin of the hill-stream fauna ... ... ... ... 58 



Means of dispersal ... ... ... ... ... 60 



Methods of propagation ... ... ... ... 61 



INTRODUCTION. 



Although in recent years considerable advance has been made 

 in the study of animal adaptations to different types of environ- 

 ment, little attention seems to have been paid to the wonderful 

 modifications exhibited by the fauna of mountain torrents. Ex- 

 cept for a few casual remarks found in descriptions of hill-stream 

 fishes, no detailed account, so far as I know, has been published 

 of the subject. Nikolsky ' in 1891 published a paper dealing 

 with the correlation between the shape of the body of fishes and 

 the strength of the current of streams and Annandale, 2 in two 

 recent papers, has described some adaptive features in the fauna of 

 hill-streams. Nikolsky's paper is unfortunately in Russian and is 

 not available in Calcutta. From Annandale 's papers I have 

 received much help. Dr. Annandale has visited a large- number of 

 hill-streams in India and elsewhere, and was greatly impressed 

 by the interesting adaptations exhibited by the various groups 



1 Nikolsky, Rev. Soc. Nat. S. Petersb., pp. 137-139 (1891). 



2 Annandale, Rec. hid. Mus. VIII, pp. 29-32 (1912), and ibid., XVI, pp. 

 113-117 (1919)- 



