Barney and Anson. — The Top-Minnow 



277 



sixty day output, and capacity of the ponds in raising and sup- 

 porting Gambusia life. The effect of predacious fish had been 

 eliminated from consideration in the 1918 fish-cultural obser- 

 vations. The 1919 oxygen determinations had also been made 

 in similar ponds, in the same water system, and in three of the 

 four ponds with vegetative environmental features exactly alike. 

 The period in 1919 during which observations on oxygen con- 

 tent of the ponds were made was approximately the same as 

 that in which the fish-cultural study was carried on in 1918, 

 the oxygen determinations beginning the last week in June, 

 1919, while the fish cultural studies began on July 1, 1918. On 

 the basis of these facts a direct comparison of the observations 

 of the two years seems to be warranted. 



The results are shown in tabular form as follows : 



Relation of Aquatic Plants to Oyxgen Supply and to Capacity of 

 Ponds to Support the Top-Minnow, Gamhtisia affinis 



Vegetable environmental features 



Surface 

 vegetation 



None 



None 



Trailing Jussiaea dif- 

 fusa 



Mat of Lemna, 

 Wolfiia and Spiro- 

 dela 



Mat of Lemna, 

 Wolffia and Spiro- 

 dela 



Submerged 

 vegetation 



Ceratophyllum 

 None visible 



None visible 



None visible 



Ceratophyllum 



Dissolved oxygen. 



Parts 



per million 



S.72 

 4.88 



0.26 



1.23 



Gambusia 

 production 



2575 

 1361 



1040 



247 



CONCLUSIONS 



In general terms of fish culture, there appears from the 

 cited data to be a correlation between the habits of growth of 

 certain aquatic plants in ponds,' the dissolved oxygen content of 

 the water, and the capacity of ponds to support plankton feed- 

 ing fishes. 



Specifically, there is a direct correlation between the pres- 

 ence of the submerged aquatic plant Ceratophyllum in a small 



