The fish studied are from three ecologically distinct estuarine niches. 

 Striped bass, a major sport and commercial fish, are anadromous and use 

 the estuary as a spawning and nursery area (Talbot, 1966). White perch 

 make semianadromous migrations (Mansueti, 1964) and are usually restricted 

 to a certain segment of the estuary throughout their lifespan. Toadfish 

 are sedentary, demersal fish and inhabit the sediment-water interface. 



The swimming abilities of striped bass and white perch suggest that 

 during periods of high turbidity these fish can move to more favorable 

 areas. However, in laboratory experiments that prevented escape, suspen- 

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

 oxygen consumption at controlled levels of swimming activity. Respiratory 

 responses of striped bass and white perch to suspended solids were observed 

 in the laboratory at concentrations exceeding those which occur naturally 

 in estuaries. These concentrations m.ay occur temporarily near dredge dis- 

 charges. 



Toadfish exhibited no significant respiratory responses to suspensions 

 of fuller's earth or natural sediment. The sediment-water interface is 

 characterized by periods of low oxygen concentration, high turbidity, or 

 both. Hall (1929, 1930) reported that oxygen consumption of toadfish is 

 almost directly proportional to the oxygen tension of the water, and that 

 the fish are able to remove all the oxygen from a limited volume of water 

 before respiratory movement ceases. This may explain the absence of re- 

 sponse. 



Suspension concentrations produced by dredging operations probably 

 have a limited effect on striped bass and white perch respiration because 

 of the mobility of these species. Toadfish are sedentary, but their high 

 tolerance to suspended solids may minimize the effects of suspended solids 

 on their respiration. 



VI. SUMMARY AND CONCLUSIONS 



Suspensions of particulate matter deposited in estuarine systems by 

 nature or man can affect estuarine fish. Stress from suspended sediments 

 may cause changes in growth, survival, and reproduction of fish. The 

 effects of suspended particles on fish depend on the concentration and 

 composition of the particles and the stress tolerance of the fish. Sus- 

 pensions of commercial mineral solids were tested to determine the effects 

 of suspended sediments of known composition, particle-size distribution, 

 and organic matter content. Additional tests were run with resuspended 

 Patuxent River estuary muds to test the effects of a natural sediment. 



Exposure to sublethal suspended solids concentrations increased micro- 

 hematocrit, hemoglobin concentration, and red blood cell count in white 

 perch, hogchoker, mummichog, and striped killifish. Increases in these 

 hematological parameters raise the blood's oxygen exchange capacity. 

 Hematological values probably change in response to suspended solids' 

 interference with oxygen-carbon dioxide transport at the gill. No signifi- 

 cant increases occurred in striped bass, spot, or toadfish. 



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