are moderately resistant to polluted waters 

 (Hart^al_. , 1945), and are adaptable to labora- 

 tory conditions of temperature, food, and 

 handling. Their small size ana availability are 

 also important factors . They thrive under 

 crowded conditions, are inexpensive, and can 

 tolerate temperatures from 65° to 100" F. 

 (U.S. Fish and WildlifeService, I960). For the 

 experiments under consideration, the small 

 size, and rapid growth and reproductive rates 

 were primary factors in the choice of the guppy 

 as a test fish. TTiey have also been used by 

 other workers in bioassay studies (Warren 

 et_aL,, 1958; Henderson e^aL, 1959a, b). 



In order to determine sublethal dosages 

 of DDT, 14 day bioassays were conducted under 

 standard conditions using trout and guppy fry 

 and adult guppies. Once the sublethal dosage 

 for the adult guppy was determined, a series 

 of sublethal dilutions of DDT was set up to ob- 

 serve the guppies over a more extended period 

 of exposure to DDT. Less extensive studies 

 were conducted to observe the possible effects 

 of the DDT on growth and survival of guppies 

 born in the toxicant and the effects of gradually 

 increased concentrations on sensitivity or resist- 

 ance to the DDT. The brain, liver, kidney, and 

 intestine of the trout fry and adult guppies were 

 prepared for histological examination in order 

 to determine the histopathological conditions 

 resulting from the presence of DDT in the organ- 

 ism. 



MATERIALS AND METHODS 



The bioassay procedures in this study 

 were conducted in accordance with the standard- 

 ized methods as far as they were applicable . A 

 stock solution of 250 milligrams technical DDT^/ 

 in 25 cc acetone solvent (Fisher certified re- 

 agent) was used for all the tests (recommended 

 by Cope^al_., 1947). 



The test water for bioassays is of 

 particular importance. It must be ideal for 

 the fish in the absence of the toxicant under 



investigation. The water used in all the bio- 

 assays came from a deep well near the 

 Connecticut River by South Hadley, Massachu- 

 setts. Use of this water source avoided the 

 fluctuation of water characteristics such as pH, 

 alkalinity, and hardness which occurs in city 

 water(Farris, 1950). Well water such as this 

 which lacks high mineral content is considered 

 satisfactory for guppies (U.S. Fish and Wildlife 

 Service, 1960). The pH of the water was 8.4. A 

 pH of 7 is ideal for trout, while a range of 6 . 7 - 

 8.6 is recommended for guppies (Turner, 1937). 



In order that gases in the water might 

 come to equilibrium with gases in the atmos- 

 phere, the water was allowed to stand in open 

 glass vessels for a minimum of 7 days before a 

 test was begun. To offset any possible decrease 

 in oxygen level which might result from the 

 addition of acetone (Henderson, et al., 1959a) air 

 was vigorously pumped through the water for at 

 least one hour before the tests. Carbon dioxide 

 level was not measured since this gas remains 

 at a sufficiently low level if the water contains 

 sufficient oxygen. 



Bioassays with the guppy 



In the experiments involving adult 

 guppies, light^temperature, food, water, oxygen, 

 and sex ratio were as advocated by Gordon (1955; 

 also SilUman, 1948; U.S. Fish and Wildlife 

 Service, 1960; Breder e^aL, 1932; Gibson et ah , 

 1955). Fifteen watt candelabra Light bulbs were 

 suspended 7-1/2" above the water in the aquaria 

 and turned on approximately 13 hours a day. 

 Temperature, checked at least twice daily, 

 averaged between 23° and 25° C, ideal for 

 guppies, with variations for short periods from 

 21° to 27° C. Though temperature is usually 

 kept within a variation of + 1° C in controlled 

 experiments, a constant water bath was not 

 available and the variation of + 3° C was well 

 within the temperature range in which guppies 

 thrive (72° - 82° F). Food consisted of dried 

 commercial aquarium food daily with white 

 worms, Enchytraeus, twice a week . A varied 



3/ Technical DDT, or C14H9CI5, is a white powder, soluble in most 

 organic solvents, but not in water. It is 76 percent p, p'isomer, 

 25 percent o, p'isomer . The DDT used in the experiments came 

 from a commercial supplier, the Diamond Alkali Company. 



