1110 



U. S. BUREAU OF FISHERIES 



prevent the use of a seine and may have an adverse effect on the 

 fish and other animal life. Removal of this excessive plant <rrowth 

 by the usual means is a very laborious process and is also hi*jjhh^ 

 objectionable for other reasons. A chemical treatment which will 

 destroy the coarser plants without injury to the fish or serious inter- 

 ference with the food supply would be a jj^reat help in utilizintij the- 

 sloughs for fish propagation. 



During the past summer preliminary experiments in treating the 

 sloughs with sodium arsenite gave most encouraging results. It 

 was found that a solution of this chemical when sprayed on the sur- 

 face of the water in sufficient (juantities to produce about 2 parts of 

 arsenic trioxide to a million parts of water caused the destruction 

 of such plants as Cemtophylluui demei'sum^ Fotamogeton interiory 

 P. fo/zosi/s, Ileteranthera duhia^ and Klodea canadensis. The ef- 

 fects of tlie tivatnient are apparent within two or three days, when 



I'niiKK 9. Installing a Hoson frv trap for tho rapturo of fry from a slongli sto;ked 

 with adult black bass, L'pi^'r ' Mississippi Wild Lif<; and Fish liefuge. The fry 

 are tlien removed to rearinjr ponds vvhiMc tliey arc frci' fioiiv tli!' danger of being 

 eaten by their hungry parents or by other spec-ies 



the plants sink to the bottom and decay. Of course the decompo- 

 sition of the plants will remove dissolved oxygen from the water, 

 and there is danger of deficiency of this gas when the ti'eatment is 

 administered to dense vegetation. In only one case was there any 

 evidence that the fish were injured by the treatment and in this in- 

 stance, owing to the large amount of vegetation present, the use of 

 the weed killer was followed by a marked oxygen deficiency. 



Plankton and bottom samples were collected in ponds treated 

 with sodium arsenite. but the study of these has not yet been com- 

 ideted. However, some preliminary examinations of the collections 

 indicate that some of the plankton organisms increased and others 

 decreased as a I'esult of the treatment. 



Recently Dr. A. H. Wiebe has conducted a series of experiments 

 at the P'airport station on the effects of arsenic on fish in aquaria. 



