A series of six concrete-bottomed daphnia ponds (fig. 2) 

 measuring 25 by 8 oy 3 feet (surface area 200 square feet, volume 450 

 cuoic feet) were found to be ideal for many of the experiments, 

 especially when replications were desired. Upon completion of an 

 experiment, each pond was drained, the sides and bottom scraped, 

 brushed, and thoroughly rinsed with fresh water before refilling. 



Experiments were also conducted in glass aquaria of 5 to 10 

 gallons capacity. At the conclusion of an experiment, each aquarium 

 was washed with a saturated salt solution, scrubbed with cleanser, 

 and rinsed with acetone and water. 



A few experiments were conducted in concrete racevrays (fig. 3), 

 each of whicn has an area of 0.023 acre, a volume of about 1,350 

 cubic feet of water and a continuous flow through the pond. 



The following DDT formulations were used in the experiments : ' -'^ 



Fbrmula 1: 25 percent wettable powder (commercial product). 



Formula 2: 50 percent wettable powder (commercial product). 



Formula 3: 50 percent v/ettable powder (commercial product of 

 ahother company). 



Formula 4: 90 percent wettable powder formulated by the Division 

 of Insecticide Investigations, Bureau of 

 Entomology and Plant Quarantine. 



Formula 5: one pound DDT, 2 pints xylene, and fuel oil No. 2 

 to make one gallon. 



Rjrmula 6: one pound DDT, 3,180 milliliters of napthenic sol- 

 vent (PD-5/^Z-B) and fuel oil to make one 

 gallon . 



Experiments with Young Fishes 



Suspensions 



Rainbow ( Salmo gairdnerii ) . brook ( Salvelinus fontinalis ) , and 

 Drown trout C Salmo trutta ), 1.5» 1.^ and 1.5 inches, respectively, ■■.,> 

 were exposed to a concentration of 0.25 pound DDT in suspension per 

 acre (0.15 p.p.m.). Seven aquaria, including one control, each con- 

 taining 1P> liters 01 water were stocked vfith three fisn of each of 

 the above soecies. The aquaria were filled and stocked March 8 and 

 sprayed with wettable DDT (formula 2) by means of a hand atomizer on 



