202 INDIAN FRESH- WATER FISHES. 



As a rule it would seem advisable to employ for 

 stocking ponds such, species as naturally thrive 

 best in the same part of the country, as these are 

 more likely to succeed than species imported from 

 other districts. It is not easy to tell beforehand 

 what conditions are necessary for any particular 

 species to live and breed, and especially to thrive, 

 as they may be able just to exist without attaining 

 the size or quality that they would do in their 

 natural location. In places where particular species 

 do not occur naturally, it would seem probable that 

 the conditions are not favourable to them, unless 

 any special reason is apparent for their non-appearance. 



We are led to this inference by finding so many 

 species in places that happen to be suited to them 

 all over the Indian continent, though not to be found 

 in intermediate localities, and also by the paucity 

 of cases in which any species is confined only to one 

 river- system or district. 



I am alluding here only to Indian species. There 

 might be among the Himalayan ranges many streams 

 admirably adapted to European fish, such as trout, but 

 no one would expect to find them there for this 

 reason only. But if it were an Indian fish in 

 question, I should say that the fact of any par- 

 ticular species not being found in a stream would be 

 a good prima-facie reason for concluding that the 

 stream was not adapted to the requirements of that 

 species, and that even if it were introduced from 

 elsewhere it would not get on well therein. 



