American Fisheries Society 12!) 



A series of Ijottom temperatures will serve to indicate the pres- 

 ence of bottom springs. 



A wide area of shallow Avater in a pond not Avell supplied by 

 sjirings 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 

 waters. Below six or eight feet the temperature decreases at the 

 rate of aljout 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 embankments. 

 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 pond weeds will serve for this purpose. 

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

 large fishes and should be introduced. If the pond be very 

 small and unshaded, some floating l^oards 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 should be removed with a seine if it is possible to 

 do so, and marketed. It is important that the mature fish crop 

 of a pond be utilized and the young of the year be given a chance 

 to develop. The accumulation of large fishes serves no useful 

 purpose, but results in overstocking, exhaustion of the food 

 supply, cannibalism and stunted growth. 



If a natural lake or pond is already stocked with carp, which 

 are not desired and can not be entirely removed, tlieir further 

 increase may be checked by the introduction of black bass which 

 feed freely on young carp. Black bass will also keep other 

 species in check by devouring their young, and thrive amazingly 

 in the process. If tlie waters contain black bass, or other fishes, 

 which have become stunted from overcrowding and the exhaus- 

 tion of the natural food supply, it is important to reduce their 



