, HABITS, BREEDING, ETC. 197 



traps, a large proportion are of species that would 

 never attain a large size, or be of any importance as 

 food. 



To sum up, it seems that the fish supply of any 

 district or river system is limited. 



First, by the amount of water available for the 

 fish during the winter, when the rivers are at their 

 lowest. 



Secondly, by the supply of food available for the 

 fish. Some kinds, as the Siluroids and Ophioce- 

 phalidse, are chiefly carnivorous ; others, as the 

 Cypriniclse, feed on both vegetable and animal 

 food. The former are mainly dependent for food on 

 the smaller species which swarm in great profusion 

 everywhere, or on the young fry of their own and 

 other species or on frogs. The latter live chiefly on 

 water-weeds and other vegetables, and consume also 

 a vast quantity of water-snails and insects. 



Thirdly, the supply of fish may be checked at the 

 fountain-head by artificial interference with the con- 

 ditions necessary to their reproduction, owing to the 

 ignorance, cupidity, or apathy of the people of the 

 country or their rulers. 



Perhaps the most mischievous habit in this respect 

 is the custom of poisoning streams which prevails in 

 many hill districts. By this means every fish, large 

 or small, in the water is destroyed, and it may be 

 years before the fish supply in that stream can recover 

 itself. 



It would be a mistake, however, to condemn even 



