Adrenal tissue: --The adrenal tissue of 

 the bony fish is characteristically scattered as 

 epithelial whorls in the kidney tissue Brown, 

 1957; Andrew, 1959). The solid, epithelial 

 masses of cells found in the kidney of the trout 

 and guppies and tentatively identified as adrenal 

 tissue were markedly affected by exposure to 

 DDT. Necrosis of this tissue (more severe in 

 the guppies than in the trout) resulted in a foamy 

 appearance (figs. 14 and 16) in contrast to the 

 solid structure characteristic of the normal 

 animals (figs. 13 and 15). In the kidney of the 

 experimental trout fry, the only region with 

 adrenal -like epithelial cells was in the middle 

 portion around the central blood vessel (fig. 16). 

 The cells, though in a disorganized state, looked 

 healthy, and their position near the blood vessel 

 was evidence either of recovery or of incomplete 

 destruction originally. 



Macroscopic observations of the guppy 

 spleen; --In dissection of adult guppies killed 

 in DDT, it was noted that the spleens were 

 generally much smaller than in the normals, and 

 the bright red color of stored red blood cells 

 was present only in spots or absent entirely. A 

 depletion in the red blood cell content of the 

 spleen was found by Baxter (1959) in lambs poi- 

 soned with aldrin and attributed to the withdrawal 

 of red blood cells from the stock in the spleen to 

 replace cells lost through congestion in the lungs 

 and hemorrhagic conditions throughout the body. 



DISCUSSION 



Evaluation of bioassay data 



The bioassay procedure as applied to 

 long-term experiments of chronic exposure is 

 not entirely reliable. Few similar tests have 

 been conducted previously, and a standardized 

 long range procedure has not been developed. 

 The concentration of DDT probably does not 

 remain constant, and it is assumed that the 

 DDT was gradually removed from the water, 

 by adsorption onto the glass, concentration in 

 the fish tissues, and perhaps lost to some extent 

 in the filtered organic wastes (Garner, 1957). 

 As the tests were intended to simulate what 

 might occur after one spraying of DDT in the 



field, it was not desirable to apply a continuous 

 flow of DDT test solution. The data do not 

 represent fish under constant exposure to a 

 specific concentration, but rather fish in water 

 treated once with a certain concentration of DDT. 

 Doudoroff (1953) also did not renew the test solu- 

 tions for 10-day bioassays. A comparison of the 

 laboratory stock solution two months after its 

 preparation with a freshly made solution on adult 

 guppies showed no difference in toxicity of the 

 two solutions . 



There was close correlation of the TL/m 

 values determined in the 14-day tolerance tests 

 on adult guppies with those reported by Henderson 

 etal., (1959a). The deviation from Henderson's 

 value of .028 ppm for the 7-day TL/m for guppies 

 in soft water was -.009 ppm or 13 percent lower 

 (.0195 ppm). The test with a second and obviously 

 more resistant strain yielded a value greater than 

 .032 ppm as the 7-day TL/m. This variation in 

 values indicates the fallacy of designating any 

 specific concentration as the TL/m. One may 

 specify a certain range of concentrations as having 

 a known toxicity, however, such as .032 ppm to 

 .018 ppm for the 7-day TL/m for guppies. Before 

 designating a safe concentration for specific fishes 

 in a locale to be treated with an insecticide, it 

 would be imperative to conduct a preliminary test 

 on a representative fish sample in the particular 

 receiving water . 



There seems to be no immediate explana- 

 tion for the increased resistance to DDT once fish 

 have been exposed to sublethal doses. As indi- 

 cated by the histopathological conditions discussed 

 later, the action of DDT seems to have only a 

 destructive effect on the tissues and a later in- 

 crease in dosage would only accelerate tissue 

 necrosis . 



The 30-day test of chronic exposure to 

 DDT in dosages sublethal to guppies at 14 days 

 demonstrated that the TL/m value determined 

 for 14 days (.018 ppm) applies to even longer 

 periods of exposure under the same conditions. 

 The loss of the fish which occurred twice after 

 a 30 -day period in the original test water might 

 possibly be avoided by completely replacing the 

 test solutions with fresh DDT solutions, perhaps 



10 



