2. Methods . 



Hematological studies of the seven fish species were conducted in both 

 an experimental tank and a control tank. Each species was exposed to a 

 concentration of fuller's earth or natural Patuxent River sediment which 

 had caused less than 10-percent mortality, and was no greater than the 

 previously determined 24-hour lethal concentration for 10-percent mor- 

 tality (LC^o) for each species (O'Connor, Neumann, and Sherk, 1976). A 

 quantity of fuller's earth sufficient to maintain the desired concentra- 

 tion was placed in the experimental tank and mixed by submersible pumps 

 for 24 hours before an experiment. The control tank did not contain 

 fuller's earth. Mineral solids were maintained in suspension throughout 

 the experiment in the two tanks by continuous pumping and aeration. 



Twelve or 15 fish were placed in each of the tanks during a test. 

 Blood samples were taken from at least 10 individuals selected at random 

 from the tanks after the exposure period. The samples were obtained from 

 white perch and striped bass by severing the second branchial artery on 

 the right side (McErlean and Brinkley, 1971), and from hogchokers, spot, 

 and killifish by severing the caudal peduncle with a heparinized blade.' 

 Blood was collected in heparinized pipets and, when possible, was mixed 

 before samples were removed for analysis. 



Microhematocrit was determined according to methods outlined by Hesser 

 (1960) . Hemoglobin concentration was estimated by the cyanmethemoglobin 

 method with modifications as suggested by Larsen and Snieszko (1961) . Red 

 blood cells were counted at X 100 on an improved Neubauer hemacytometer, 

 using a modified Hayme's solution as the dilution medium (Heinle and 

 Morgan, 1972) . Whole blood osmolality was measured with a freezing-point 

 depression osmometer. 



3. Results and Interpretation . 



Hematological characteristics of white perch, hogchokers, and striped 

 killifish changed in response to sublethal concentrations of suspended 

 solids. The effects of these sublethal concentr^ations were analyzed 

 extensively for white perch (Table 1). Exposure of white perch to 0.65 

 gram per liter (g 1"^) fuller's earth for 5 days resulted in significant 

 increases in microhematocrit, hemoglobin concentration, and red blood 

 cell count. The ionic concentration of the blood, estimated by whole blood 

 osmolality, did not change. 



There was a relatively greater increase in red blood cell counts than 

 in microhematocrits and hemoglobin concentrations. The increase in red 

 blood cell count for experimental groups was 30 percent greater than the 

 increase for control groups. Hemoglobin concentrations increased by 15 

 percent; microhematocrit values exceeded those of control fish by 17 

 percent . 



10 



