HABITS, BBEEDING, 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- 
phalidee, are chiefly carnivorous ; others, as the 
Cyprinidse, 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 
