276 American Fisheries Society 



Oxygen Record of Ponds in 1919 



It is reasonable to believe that pond 1 should have been 

 observed to have dissolved in it a larger quantity of oxygen than 

 pond 2, and pond 3 more than pond 4, from the fact that ponds 



1 and 3 contained abundant submerged plants, whereas ponds 



2 and 4 had none. It plainly indicates the value of submerged 

 plants in oxygenating ponds. That ponds 1 and 2 should both 

 have had higher dissolved oxygen records than ponds 3 and 4 

 is logical, since their surfaces were open to allow for wind 

 action and for the penetration of the sun's rays to assist in 

 photosynthesis, while ponds 3 and 4 were covered with a heavy 

 surface growth that permitted no wave action and allowed a 

 mimimum of sunlight to pass through to cause photosynthesis 

 in those plants which may have been beneath the mats. 



These ponds were stocked similarly to those of 1918, but 

 their larger size (30 x 50 x 5 feet) and the physical impossi- 

 bility of drawing a seine through them because of immovable 

 snags, or of clearing them of fish with a dipnet, led to giving up 

 the idea of noting their production. Such ascertainment of 

 the output of Gambusia of these ponds would have been of 

 minimum value for our purpose under the conditions, since the 

 effect of predacious fishes could not be eliminated or measured. 



The oxygen determinations and the differing plant combi- 

 nations of 1919 were, however, available for comparison with 

 the results of the 1918 experiments in numbers of fish in the 



