14 



CIRCULAR 15, FISH AND WILDLIFE SERVICE 



Chlordan is less toxic to fishes 

 than is DDT but more toxic than 

 benzene hexachloride. Applica- 

 tions of 1 pound to an acre to out- 

 door ponds killed 87 percent of the 

 bluegill sunfish. With applica- 

 tions of 0.5 pound to an acre most 

 of the bluegills as well as other 

 species survived, and v^^ith those 

 of 0.25 pound to an acre practi- 

 cally all fishes survived. A 12-per- 

 cent chlordan solution (w^t/vol) in 

 fuel oil was used in all applications. 



TEPP (Tetraethyl-pyrophos- 

 phate). Tests with TEPP indi- 

 cate its toxicity to fishes is com- 

 parable with that of DDT. Con- 

 centrations of 0.25 p. p. m. or more 

 were found to be lethal in aqua- 

 rium tests. 



Parathion. In the purest form 

 available parathion did not kill 

 one-inch rainbow and brown trout 

 at 0.063, 0.189, and 0.378 p. p. m. 

 Experimental work on the effects 

 of this insecticide has not been 

 completed. The observation, how- 

 ever, that 0.2 p. p. m. is near the 

 threshold point for bluegills was 

 confirmed. Preliminary experi- 

 ments with 25-percent emulsi- 

 fiable parathion powder on blue- 

 gill sunfish showed scattered mor- 

 tality at 0.1 and 0.2 p. p. m., and 

 approximately 50 percent mortal- 

 ity at 0.3 p. p. m. 



Bis (p-chlorophenoxy) methane 

 was tested only with bluegill sun- 

 fish approximately 1 inch long. 

 There was no mortality at 0.05 

 p. p. m., and very low mortality at 

 0.10 p. p. m. All fish treated died 



when the concentration reached 

 0.2 p. p. m. 



EFFECTS OF DDT ON OYSTERS 



DDT is being widely used for 

 mosquito control in many salt- 

 water areas and for control of flies 

 in fish-packing areas. The spray- 

 ing of piles of oyster shells with 

 DDT to eliminate fly nuisance is a 

 rather common practice. As these 

 same shells may be used as cultch 

 for a new generation of oysters, it 

 is important to know whether 

 spraying them with DDT will in- 

 hibit their later use for collecting 

 young oysters. 



To determine some of the rela- 

 tionships between insect control 

 through the use of DDT and oys- 

 ter management, a number of 

 studies were carried on at the Mil- 

 ford Biological Laboratory, Mil- 

 ford, Conn. The results of these 

 investigations have been reported 

 in a manuscript * prepared for 

 publication by V. L. Loosanoff, 

 C. A. Nomejko, and F. D. Tom- 

 mers, from which the following 

 summary is taken: 



Neither DDT nor kerosene alone 

 substantially depressed the rate 

 of setting of oysters, but the com- 

 bined effects of DDT and kerosene 

 reduced the setting on shells 

 dipped for 30 seconds in a 5-per- 

 cent solution of DDT in kerosene. 



The effect of the DDT solution 

 was not noticeably diminished 

 even when shells were dipped in 

 the solution several weeks before 

 planting them. 



* Effects of DDT on oysters, by V. L. Loosanoff, 

 C. A. Nomejko, and F. D. Tommers. [Unpub- 

 lished.] 



