270 American Fisheries Society 



Pond 1. Supplied abundantly with the submerged aquatic plant Cera- 

 tophyllum. Surface kept entirely open and clear of all surface- 

 growing plants. 



Pond 2, Kept entirely clear of all visible vegetation. 



Pond 3. Supplied with a quickly and thickly growing surface-trailing 

 plant, Jussiaea diffusa. No other surface plants present; no sub- 

 merged plants present. 



Pond 4. Supplied with a heavy surface covering of Lemna and Spiro- 

 dela, in which Wolffia filled in the interstices between the leaves of 

 Lemna and Spirodela. 



After removing predacious species, there were introduced 



into each of these ponds ten male and forty female 



Gamhusia affinis, all adults, the females being heavily gravid. 



The date of this stocking was July 1st. On September 1st, 



sixty days afterward, the ponds were seined, with results as 



follows : 



Gambusia Production of Ponds in 1918 



Pond Gambusia 



No. Surface vegetation. Submerged vegetation. production. 



1. None. Abundant Ceratophyllum. 2575 



2. None. None visible. 1361 



3. Trailing plant Jussiaea None visible. 1040 



diffusa. 



4. Heavy mat of Lemna, None visible. 247 



Spirodela and Wolffia. 



The ponds, averaging in content about 450 cubic feet, had 

 doubtless reached their capacity for supporting animal life; 

 and a further month's opportunity for increased output would 

 have changed the above figures very little. 



These results quite plainly indicate the effect aquatic vege- 

 tation may have in partly supplying fish with the conditions 

 which best suit their requirements. The pond having the 

 submerged vegetation produced a much greater output than 

 any of the others, the production decreasing by approximately 

 half in the pond with the open surface and the pond with 

 the surface trailing Jussiaea diffusa. The pond having the 

 heavy surface mat of Lemna, Spirodela, and Wolfifia seemed 

 to be least able to support Gambusia life. 



