94 >^EW YORK ZOOLOGICAL SOCIETY. 



attempt it. but interest in most things comes with learning about 

 them, so the books should be read at the beginning — not after fail- 

 ures have led to discouragement. 



Xatiiral Ponds or Lakes. — It is assumed that the position of the 

 natural pond is such that no arrangement can be made for drawing 

 off the water. Its possibilities will therefore have to be consid- 

 ered separately. Its fish life moreover can never be brought under 

 complete control. 



If the character and abundance of the fish life in the pond are 

 not known it is desirable that it be ascertained as far as possible 

 by fishing or netting. If the pond is without any fishes it should. 

 of course, be stocked at once, and the selection of fishes made with 

 due regard to its natural conditions. The extreme depth, mid- 

 summer temperature, plant life and character of the bottom of the 

 pond should all be ascertained. The summer bottom temperature 

 of deep ponds should be known. It can be taken by lowering the 

 thermometer in a pail and allowing it to remain some time. If 

 pulled up rapidly the temperature will not have time to rise ma- 

 terially. A series of bottom temperatures will serve to indicate 

 the presence of bottom springs. 



A wide area of shallow water in a pond not well supplied by 

 springs or rivulets usually means great warmth in summer. If 

 such a pond can be temporarily lowered and deepened in places, 

 its conditions for fish life would be greatly improved as there 

 is a decided difference in temperature between surface and 

 bottom w^aters. Below six or eight feet the temperature decreases 

 at the rate of about two degrees for each foot of depth. Increased 

 depth would also give fishes an additional chance for life in 

 winter when heavy ice diminishes their supply of air. 



A small pond, supplied chiefly by rainfall, may be increased 

 somewhat in water supply by leading to it ditches from adjacent 

 fields ; while its depth may admit of some increase by embank- 

 ments. If water can be had by boring, an artesian well may make 

 just the difference between a poor pond and a good one. Fish- 

 ponds should have water plants to afford shelter for young fishes 

 and harbor the various forms of aquatic life on which they feed. 

 Several kinds of common pondweeds will serve for this purpose. 

 The broad leaves of water-lilies afford shelter in summer for the 

 larger fishes and should be introduced. If the pond be very small 

 and unshaded, some floating boards will afford shelter. Too many 

 large fishes in the pond are detrimental since they are consuming 

 the food supply and are themselves going to waste. When such 

 fishes can not be taken with the hook as sometimes happens, they 



