of repeated sublethal doses of pesticides on 

 survival, growth, and reproductive potential, 

 through at least one reproductive cycle and 

 with the use of histology and hematology as 

 tools are also in process there (vonLimbach, 

 1969^. Some studies of inhibitory effects of 

 DDT on reproduction of quail, pheasants, and 

 dogs (De Witt, 1955, 1956; Rudd^LaL, 1956a, h; 

 and Kitselman, 1953, respectively) have already 

 been reported, and a possibility of similar 

 effects on fish and wildlife seems unquestion- 

 able. 



A standardized procedure and means 

 of interpreting data were found to be essential 

 for comparing results of different workers, and, 

 to avoid the discrepancies in toxicity values 

 reported by the first investigators in this field. 

 The first effort to standardize bioassay methods 

 was made by Hart et al. (1945). This procedure, 

 simplified by Doudoroff ^ al_. (1951, in affiliation 

 with the toxicity subcommittee of the Federation 

 of Sewage and Industrial Wastes Association), is 

 followed by most industries which test the toxic- 

 ity of their wasteson fish (U.S. Public Health 

 Service, 1956, 1957). The method is simple and 

 yielas reliable, reproducible results. 



The bioassay procedure involves placing 

 the fish in serial dilutions of a toxicant and 

 recording the percent survival in each concen- 

 tration at specified times . The dilutions are 

 generally in a logarithmic series for ease in 

 plotting results . To express the effects of a 

 substance on fish, a value termed the tolerance 

 level median (TL/m) has been used by various 

 workers (State Water Pollution Control Board, 

 1952; Tarzwell, 1957a, b). This value is the con- 

 centration of the substance under investigation 

 in which 50 percent of the test animals are able 

 to survive for a specified period of time under 

 the conditions of the experiment. 



Studies to determine the methods of 

 action of DDT and other insecticides on fish 

 and wildlife have also involved both biochemical 



and histological investigations . The chlorinated 

 hydrocarbons such as DDT are readily concen- 

 trated in fish, especially in the fatty tissues 

 (Garner, 1957; Cope, 1959), but seem to be of 

 little harm to the fish in low concentrations. No 

 complete survey of histopathological conditions 

 occurring in fish exposed to chlorinated hydro- 

 carbons was found in the literature, though fairly 

 extensive work has been done by Baxter(1959) on 

 lambs exposed to aldrin, by Kitselman (1953) on 

 dogs exposed to aldrin and dieldrin, and by Bell 

 (1961) on goats exposed to DDD. The external 

 signs of stress in animals exposed to some of 

 the chlorinated hydrocarbons, and histopatholog- 

 ical conditions involving particularly the 

 degeneration of the zona fasiculata of the adrenal 

 gland and severe liver and intestinal disturbances 

 have lead various workers to suggest a direct 

 inhibitory effect of the insecticides on adrenal 

 tissue (Nelson ^al_., 1949; Gowdey et al . , 1955; 

 and Bell, 1961). Modification of the normal enzyme 

 system and metaboUc pathways by insecticides is 

 being investigated at present by Hosein (reported 

 by Weiss, 1960). 



The present study was undertaken to 

 determine the effects of chronic exposure of 

 DDT on fish, using the guppy (Lebistes retic - 

 ulatus) as the basic laboratory test animal and 

 correlating results with those obtained using the 

 local brown trout fry (Salmo trutta) . 



Henderson etal_., (1957) state, "While 

 they (guppies) are not of economical or recrea- 

 tional importance in receiving waters and 

 biological assay results may not be applied to 

 other fish directly, guppies are among the most 

 desirable form from the standpoint of mainten- 

 ance in the laboratory and uniformity of available 

 stock. If provision is made for comparison with 

 important local species under similar conditions, 

 the guppy may be considered a .desirable test fish 

 for routine biological assay work." 



Guppies ( Lebistes reticulatus ) belong to 

 the Poeciliidae, a family of live bearers. They 



2/ vonLimbach, B. 1960 Communication of August 2, 1960, to Chief, 

 Fish-Pesticide Research Laboratory 



