PROGRESS IN BIOLOGICAL INQUIRIES, 1930 607 



and later with bass fry. Unfortunately shortly after the sloughs 

 were stocked with bass there was an unusually high June Hood, 

 which rose above the screens and allowed the fish to escape. This 

 occurred in five of the eight sloughs which had been stocked. The 

 remaining three sloughs all showed a good production of fingerling 

 bass. 



One slough with an area of approximatelv 4 acres was stocked 

 with 20,800 bass fry on June 15. When seined September 15-17, 

 there were 10,538 fingerlings removed, a survival of approximately 

 50 per cent. Another slough known as pond No. 2 with an area of 

 1.5 acres was stocked with 5,180 fry on June 22. The slough was 

 seined September 19, and 3,691 fry averaging 4% inches long were 

 recovered. This is a survival of approximately 71 per cent which 

 is by far the highest rate of survival obtained in any of our experi- 

 mental work. The third slough, area 1.3 acres, was used as a brood 

 pond so the number of fry in the pond is unknown. This pond was 

 seined August 20-22 and 11,422 fingerlings removed. This is at the 

 rate of 8,786 fingerlings per acre which compares favorably with 

 the production obtained in the ponds at Fairport. 



Although on account of the unusual flood conditions the total pro- 

 duction of bass fingerlings fell siiort of expectations, it is evident 

 that in ordinary seasons these sloughs can be made to produce fully 

 as many fish as the average hatchery pond. 



Since the control of aquatic vegetation is essential to the successful 

 utilization of the sloughs for the production of game fish, consider- 

 able attention has been devoted to this problem. Experiments with 

 a sodium arsenite weed killer by Mr. Surber indicate that treatment 

 of the fishponds with this chemical may furnish a solution of the 

 j)roblem. From the fish-cultural standpoint this chemical has a 

 great advantage over copper sulphate, which has been used to some 

 extent for this puri)ose, in that it aft'ects the alga? less than the 

 higher plants and is not nearly so toxic to fish. 



In the experimental work in the sloughs used as fishponds, dilu- 

 tions varying from 1 to 1.7 parts per million — depending on the 

 density of the vegetation — of arsenious oxide have been used with 

 success. It was found that the treatment did not directly destroy the 

 abunuant plankton organisms, either plant or animal. Further- 

 more, no serious effects have been produced on the abundance of 

 bottom organisms and Entomostraca except in some instances where 

 the numbers of organisms dependent on the larger aquatic plants 

 have been reduced as was to be expected. No evidence was obtained 

 in these experiments that concentrations of arsenious oxide up to 

 3.5 parts per million were toxic to fish in the slightest degree. The 

 only mortality that occurred was caused by lack of oxygen which, 

 of course, can be avoided by beginning the treatment in the spring 

 before the vegetation has become unduly abundant. 



Experiments at the Fairport station by Dr. A. H. Wiebe have 

 shown that bass, bluegills, and crappie are not appreciably affected 

 in aquaria by concentrations of AsoOs as high as 7 parts per million. 

 It is evident, therefore, that there is no danger of the fish being 

 seriously injured by the sodium arsenite treatment. Experiments 

 are now being made to determine the effect of arsenic on some of 

 the more common food oro^anisms of fish. 



