Barney and Anson. — The Top-Minnozv 269 



added to these facts, indicating the limitations of oxygen 

 supply in water, there is that of the limited capacity of water 

 to dissolve oxygen — its period of greatest capacity occurring 

 when the water is cold and when, apparently, it is of less value 

 to the fish, since metabolism of all cold-blooded animals is 

 very slight through the winter months. It seems a paradox 

 that the increased need for oxygen for metabolic processes 

 during the spring, summer and early fall should come when 

 the power of water in dissolving and in holding oxygen should 

 be continually decreasing, the capacity of water to dissolve 

 oxygen decreasing with the increasing temperature. There 

 is, however, the compensating factor of increased oxygen pro- 

 duction by submerged plant life during the warm weather, 

 which factor is negligible in winter. 



In this general connection there also arises the question 

 of the actual capacity of a pond or body of water to support 

 animal Hfe; how much fish life a body of water of given size 

 can be expected to bring to maturity and hold under certain 

 conditions where predacious species have been eliminated. 

 There is, of necessity, in this problem a consideration of the 

 means whereby, and of the quantity in which, oxygen and 

 food reach the fish, since oxygen and food, other factors being 

 the same, become, possibly, the most important criteria on 

 which the capacity of a pond may be estimated. 



EXPERIMENTAL OBSERVATIONS 



In 1918 four small ponds were built by throwing dirt em- 

 bankments across the very sluggish stream, Cypress Bayou, 

 Mound, La. These ponds average in size 30 by 12 feet, 

 varying in depth of water, because of seepage, from 10 inches 

 to 2}^ feet. The banks were kept clear of weeds, while the 

 waters were provided with four differing habitats by introduc- 

 ing into three of the ponds certain aquatic plants of different 

 habits of growth and by keeping one pond free of all vegeta- 

 tion other than microscopic. A description of the vegetative 

 environment of each pond follows: 



