The LC5qg value for white perch exposed to resuspended natural sediments 
was 19.80 g 171; the LCsg value for fuller's earth was 9.85 g Weep A 
similar range applied to LCqg and LC,q values in resuspended natural sedi- 
ments when compared with fuller's earth, and varied between 39.40 versus 
31.81 g 1°} (LCg9) and 9.97 versus 3.05 g 171 (1C)9), respectively. 
Spot exposed to natural sediments had a LCsg value of 88.00 g 12 
and LCjg and LCg9q values of 68.75 and 112.63 g 1-1, respectively, for a 
24-hour exposure. These values contrast with 24-hour values of fuller's 
Earth) at 13.81) 20.354, and 3362) for LCi/o,) LCc og, eandylGog.. hespectavelye 
Spot were previously reported to have a relatively low tolerance to resus- 
pended natural sediment (48-hour LCs5q = approximately 3 g 172) (Sherk, 
O'Connor, and Neumann, 1972). Lethal concentrations for replicated 48- 
hour exposures were essentially equal to 24-hour values. This suggests 
that (a) spot have a compensatory mechanism that allows them to tolerate 
high levels of natural suspended material for at least 48 hours, and (b) 
the preliminary results for this species (Sherk, O'Connor, and Neumann, 
1972, p.24) were in error. This error was probably caused by inadequate 
oxygenation of the experimental sediments. Spot exposed to these suspen- 
sions of natural material were observed to have a high initial oxygen 
demand. As a result, high mortality occurring in experimental tanks was 
probably caused by low oxygen concentration, not by sediment concentra- 
tions. 
The alimentary canal of fish from these bioassays was packed with sedi- 
ment. The entire digestive tract was swollen and distorted by ingested 
material. 
Separate concentration-dependent mortality determinations (48 hours, 
25° Celsius) were conducted on the common mummichog with both fuller's 
earth and natural sediment. For fuller's earth suspensions, 48-hour values 
Were-N i LGg) =) S586) gil eLGny — e45)lGl lo lie andi Co qe—564SOmpas leu 
Natural sediment concentrations could not be maintained high enough to 
cause sufficient mortality to determine lethal concentrations. Sixty-two 
percent of adult mummichogs survived concentrations greater than 125 g 1=4 
for 24 hours and 100 percent survived concentrations in excess of 109 
g 1! for 72 hours. 
Striped killifish exposed to resuspended natural sediments for 24 hours 
had LCi9, LCsq, and LCo9qg values of 97.1, 128.2, and 169.3 g 171, respec- 
tively. 
IV. DISCUSSION 
The effects of suspended natural and mineral sediments on estuarine 
fish are partially dependent on certain characteristics of the suspended 
materials. No species, including menhaden, died in suspensions of 
kaolinite clay (median particle size of 0.55 micrometer). Menhaden are 
highly sensitive to suspensions of solids other than kaolinite. However, 
suspensions of fuller's earth in concentrations exceeding 0.65 g 17! were 
