Pish Culture in Inland Waters 251 



The character of the breeding grounds may be changed or de- 

 stroyed in many ways. Sand, soil and other materials, such as saw- 

 dust and other debris, may be washed upon the breeding grounds 

 and thus make them unfavorable. Severe erosion may clog the 

 channels of streams and destroy the breeding grounds as effectively 

 as a driftw^ood dam or a beaver dam may destroy a shoal or riffle 

 in a brook or creek. Even the growth of vegetation tipon the breed- 

 ing grounds may injure them, although some fish will clear away 

 such plants when they form their nests. 



When periodical planting is intended to wholly replace natural 

 breeding conditions of course the breeding habitat is correspondingly 

 reduced in importance, but on the whole this is a very expensive 

 policy and is of very doubtful applicability to public waters. Other- 

 wise, provision for such grounds and their protection is of the 

 greatest value. The changing- conditions of these grounds, and the 

 life of the eggs and fry while upon them, are in urgent need of very 

 careful study. Today this is one of the weakest points in fish cul- 

 ture. 



Relation of Volume of Water to Capacity. It is not necessary to 

 call attention to the possibilities of depletion from unrestricted fish- 

 ing by an unlimited number of anglers. " Artificial " propagation 

 and due regard to conservation greatly reduces the danger. Yet 

 there is a limit to the efficacy of artificial stocking of waters imposed 

 by the limitations of biological capacity, the significance of which is 

 that it is possible to conceive of so many anglers that the waters 

 could not support enough fish to afford good fishing to all ; also that 

 there would be danger of overstocking in any attempt to meet the 

 demand, which sooner or later would result in general depletion. Of 

 course there is at present no generally satisfactory way to limit the 

 number of anglers in public waters, and the customary limits in size 

 and quantity of fish and in angling methods are about the only 

 feasible restrictive measures. This point, too, involves a considera- 

 tion of biological capacity. Amongst other considerations biological 

 capacity involves the volume of water and its physical characters, as 

 waters dififer not only in respect to the number of fish they can 

 support, but in the kinds of fish to which they are suited and the size 

 to which the fish can attain in them. 



In respect to volume and physical characters bodies of water 

 differ greatly. There are standing bodies of water comprising lakes, 

 ponds, pools, springs, etc., and moving waters designated as rivers, 

 streams, creeks, brooks, runs, etc., and there are waters also which 

 may be regarded as more or less intermediate between the two 

 classes. Many of these contribute to one or the other both physi- 

 cally and biologically. All of these conditions should be taken into 

 consideration in stocking, for success or failure may depend upon one 

 or another of the characters. 



Lakes and Ponds. Recent terminology affords no definition to 

 distinguish a lake from a pond. Webster's Dictionary defines a lake 

 as " A considerable body of standing water in a depression of the 



