Pesticide residues in channel catfish from Nebraska.

Channel catfish (Ictalurus punctatus) were collected in all of the major watersheds in Nebraska during the summer of 1964. Individual fat samples and composite blood samples obtained from these {ish were analyzed to determine the concentrations of residues of DDT and its metabolites (o,P'DDT, p,p'-DDT, p,p'-DDD, and DDE) and dieldrin. A total of 178 fish, collected from 18 sites, were analyzed. As expected, the fat samples contained higher concentrations of the pesticides than did the blood samples. DDT residues were found in all fat samples, and average levels from 10 fish sampled at each site ranged from a low of 2.2 ppm in the sandhills region to a high of 92.2 ppm in Salt Creek below Lincoln, Nebr. Average dieldrin residues in fat samples ranged from 0.1 to 6.7 ppm. All values are expressed as ppm (p.glg) of residue detected in each sample of fat. The composite blood samples were found to contain DDT residue concentrations ranging from a low of less than 0.01 ppm to a high of 0.16 ppm. Dieldrin residue concentrations ranged from a low of less than 0.01 ppm to a high of 0.07 ppm.