Suspensions 



On August 10, 1946, four trout racewajra (fig* J), each with 

 an area of 0.023 acre ana a water Tall of 8-12 inches oetween 

 each raceway, were stocked with trout and other fish (table 4). 

 The rate of flow in the uppermost raceyray was I30 gallons per 

 minute, wtiereas it was 80 gallons per minute in the third raceway 

 as water was lost underground through a crack in the bottom of 

 pond 2. Spraying was started at 7:20 p.m., on August 12, in tne 

 uppermost raceway, and completed in the last one 55 minutes later. 

 The wettable DDT (formula 2) spray was applied with a hand atomizer 

 at the rate oi one pound of DDT per acre (maximum possible concentra- 

 tion in uppermost pond, 0.258 p.p.m.). 



In pond 3, one small mouth black bass and one rainbow trout were 

 found dead in the morning after the spray application and may have 

 been killed by DDT. Early in the afternoon one dead golden shiner 

 was collected from this pond, and others were observed to be sick. 

 The affected fish did not school with the other fish and swami in 

 circles in an erratic manner. Seven ol 10 golden shiners killed by 

 DDT in pond 3 died within 24. hours after the spray application. For 

 some inexplicable reason, 13 of the 15 fish killed by DDT were found 

 in pond 3« Pond 4- probably received the most DDT, lor, in addition 

 to being sprayed, it received the run-off from the other three ponds. 



The experiment indicates ttiat a DDT suspension, applied at the 

 rate of one pound of DDT per acre to a flowing stream, could cause 

 negligible losses to brook and rainbow trout, smallmouth black bass, 

 and golden shiners under conditions similar to those of this experi- 

 ment. 



On August 23, 1946, each of six daphnia ponds (fig. 2) were 

 stocked with 200 fish (50 each of smallmouth black bass, largemouth 

 black bass, bluegills,, and golden shiners). Ponds 3 ana 4 were 

 treated witn suspension formula 3, ponds 5 and b with suspension 

 lormula 2, containing DDT at one pound per acre (0.I8 p.p.m.). Ponds 

 1 and 2 served as controls. The applications were made with a hand 

 sprayer on August 26. The ponds were drained September 9, The 50 

 percent wettable DDT powders of two manufacturers showed marked 

 differences in toxicity (table 5)« Possibly this was due to the 

 nature ol" the wetting agents. The survival figures for the bluegills 

 were all low due to predation on the part of the bass. lixcluding 

 fungus-killed fish ana those taken by predation, figures are given 

 in the table for those fish killed by DDT. Suspension formula 2 

 caused minor losses, whereas the suspension formula 3 accounted 

 for sizable losses of all species. Greatest mortality occurred from 

 three to seven days after treatment. This delayed action in toxicity 

 was also noted when Back Creek vr&s treated during midsummer of 194.6 

 (Hoffmann and Surber 1948). Ilovrever, in oil spray experiments in 



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