Effect of Airplane Distributed DDT Thermal Aerosols on Fish and Fish Food Organisms

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Abstract
Investigations were carried out in the Wheeler and Kentucky Reservoir areas of the Tennessee Valley during the summer of 1945 to determine the effect upon fish and fish food organisms of a formulation of 20% DDT in Velsicol NR-70 applied by airplane in the form of a thermal aerosol at the rate of 0.1 lb. DDT per acre with an average maximum recovery in the center of the swath of about 0.012 lb. per acre. The maximum effect at the center of the swath resulted in almost complete elimination of anopheline and culicine mosquitoes and surface Hemiptera and in a significant reduction in Coleoptera and amphipod Crustacea with little or no reduction of other macroscopic forms. The effect of routine treatments on an area basis was almost a complete elimination of anopheline mosquitoes and surface Hemiptera and a significant reduction in culicine mosquitoes with no evidence of reduction in other forms. Observations in areas at the end of a full season of 16 applications at the rate of 0.1 lb. DDT per acre indicated that surface Hemiptera had been almost completely eliminated and mosquitoes were considerably reduced but other forms were not significantly affected. Surface Hemiptera are not important as fish food and because of their predaceous habits may actually compete with fish for food. On the basis of these studies, it is therefore concluded that DDT applied in the manner indicated does not have any significant injurious effect upon the total population of fish food organisms. Detn. of fish populations at the end of the season in areas which had received 16 routine weekly applications of DDT thermal aerosols at the rate of 0.1 lb. DDT per acre showed an average population per acre of 12,549 fish weighing 700 lbs. From a consideration of the total number and weight, the species composition, the abundance of young-of-the-year, and the condition of the fish in comparison with those in untreated portions of the reservoirs, it is concluded that the DDT treatment had no injurious effect upon the resident fish population. The above conclusions apply only to this dosage and method of applying DDT and do not mean that increased rates of application or different methods of application might not have injurious effect upon fish and fish food organisms.