exposure to a sublethal concentration of the 

 insecticide increased or reduced the resistance 

 of the fish to DDT, those adult guppies surviv- 

 ing the 2 -week test series were transferred 

 immediately after 14 days into tanks of freshly 

 prepared concentrations of .032 ppm under 

 constant conditions . Records on survival were 

 kept for 30 days . 



Stability of the stock solution: - - To 

 ascertain if the toxicity of the stock solution 

 remained constant, the stock which had been 

 standing for two months was compared with a 

 freshly prepared stock solution. Identical test 

 solutions of .032 ppm in 3-1/2 liters of water 

 were made from each stock to which duplicate 

 sets of five normal fish from the same strain 

 were added and observed for 14 days. 



Thirty-day exposures to sublethal dos- 

 ages of DDT with some observations on growth 

 and reporduction: -- Conditions for extended 

 tests varied from the 14-day TL/m determina- 

 tions only by the use of two gallon "squash" 

 aquaria which held 7 liters of test solution and 

 10 fish per tank. No duplicates were conducted. 

 Concentrations of .0185, found previously to be 

 the concentration in which at least 50 percent of 

 the guppies could survive in a 2 -week period, 

 .010, .0056, .0018, and .001 ppm were tested 

 and a control was set up, this time adding the 

 same concentration of acetone to the control as 

 used in the .0185 ppm tank (.013 cc acetone). 



It was hoped that effect of DDT on weight 

 could be determined and the fish from each tank 

 were weighed, males and females separately, at 

 the beginning of the experiment, and at two 

 intervals of two weeks. The weight was deter- 

 mined by weighing the fish to the nearest 1/100 

 of a gram in 150 ml glass beakers with a mini- 

 mum of water. To avoid excessive handling of 

 the fish, measurements of length were not taken. 



As a result of some disease or of an 

 increasingly high level of dissolved wastes in 

 the water, the fish started to die rapidly in each 

 of the tanks including the control after 30 days, 

 and the experiment was discontinued. A repeat 

 of the test using sterilized glassware and filter- 

 ing the water every 5 instead of 7 days ended 

 also because of the unexplained deaths of the 

 fish after 30 days . 



An apparatus was designed to trap and 

 separate young born in DDT from the adult 

 guppies and consisted of a glass beaker 4" high 

 in which was suspended a glass funnel covered 

 with nylonized cloth. The beaker was set in- 

 side the larger aquarium under the usual 

 experimental conditions. Gravid guppies were 

 placed in the covered funnel, and the newly 

 born fish settled through the stem of the funnel 

 into the beaker below . Plastic traps were not 

 used as the plastic reacts with and fouls the 

 DDT test solutions, indicating possible chemical 

 changes affecting the toxicity of the solutions . 



Young guppies, born within a 2 -day 

 period 23 and 24 days after the experiment was 

 begun, were placed separately in 3-1/2 liter 

 widemouthed jars with 340 cc untreated well 

 water per fish and kept under constant conditions 

 of light, temperature, and food (dried aquarium 

 food only) for 40 days. Measurements of length 

 were taken at the end of this period. 



One to 14 -day TL/m determinations for 

 14-21 day guppy fry: -- Five 2- to 3-week- 

 old guppy fry were placed in 1700 cc of water 

 (340 cc/fish) in each of 9 widemouthed jars. 

 DDT was added in concentrations of .056, .032, 

 .018, .010, .0056, .0032, .0018, and .0010 

 ppm . Guppies of the same age in untreated well 

 water served as controls. Light, temperature, 

 and feeding conditions were kept constant. Only 

 dried aquarium food was used. Daily records 

 for survival rates were kept and any dead fish 

 removed immediately . 



Bioassays with young brown trout 



In order to have conditions similar to 

 those used on the adult guppies, 700 cc well 

 water/fish were allotted in the trout assays. 

 No mechanical aeration was used during the 

 tests though the solution was aerated prior to 

 the addition of DDT. The trout fry used in the 

 bioassays and histological studies came from a 

 local Massachusetts State Fish Hatchery and had 

 been raised in running water of approximately 

 7° C. and a pH of 7. Before the tests, the fry 

 were kept in tanks in non -circulating well water 

 (pH 8.4) at approximately 8° C. Extended 

 acclimatization to laboratory conditions was 

 avoided before most of the following experiments 



