White perch experienced gill tissue disruption and intensified mucus 

 production on the gills during exposure to fuller's earth suspensions. 

 Although fuller's earth concentrations below the 24-hour LCjq value were 

 used, the gill tissue structure of white perch was adversely effected and 

 the respiratory surface area was reduced in a 5-day period. 



High rates of liver glycogen depletion were recorded in hogchokers 

 exposed to sublethal fuller's earth concentrations. This indicates carbo- 

 hydrate utilization and drainage of metabolic reserves during periods of 

 sediment stress. Hogchokers live at the sediment -water interface, but 

 still demand extra energy for compensatory alterations of their physiology 

 while exposed to suspended sediments. 



Oxygen consumption of striped bass and white perch increased with 

 swimming speed in control tanks containing filtered river water. However, 

 suspensions of fuller's earth or Patuxent River sediments generally reduced 

 fish oxygen consumption rates at high levels of swimming activity. This 

 indicates that sediment suspensions interfered with the fish's respiratory 

 ability. Both striped bass and white perch are common to the open waters 

 of the estuary. However, toadfish, which inhabit the turbid sediment-water 

 interface, showed no significant respiratory responses to fuller's earth 

 or natural sediment suspensions. 



It is customary and useful to establish suspended solids criteria by 

 applying the lethal concentration levels causing 10- to 50-percent mor- 

 tality over a defined period of exposure. However, this procedure ignores 

 the biologically significant sublethal effects of suspended solids on 

 estuarine fish. Concentrations of suspended sediments found in estuarine 

 systems during storms, flooding, dredging, and dredged-material disposal 

 are within the range of sublethal concentrations used in these experiments. 

 Since the experimental suspensions induced stress responses in several 

 fish species, preproject evaluations of the effects of dredging and related 

 activities should include consideration of this effect. 



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