Oxygen consumption rates were determined for striped bass, white perch, 

 and toadfish in filtered Patuxent River water (base line) and in filtered 

 river water suspensions of fuller's earth or Patuxent River sediment. 



Several methods are commonly used to measure fish oxygen consumption 

 (Fry, 1971). Brett (1962) described the following three levels of fish 

 respiration, in terms of activity: 



(a) Standard oxygen consumption, required to support tissue 

 metabolism during periods of inactivity; 



(b) routine oxygen consumption, required during periods of 

 random activity; and 



(c) active oxygen consumption, required during periods of 

 swimming at moderate to maximum speeds. 



Respiration rates of pelagic fish in this report were determined under 

 conditions of moderate activity. Values reported for demersal fish are 

 measures of routine oxygen consumption. 



2. Material and Methods . 



a. Equipment . A tunnel-type respirometer (Brett, 1964), which main- 

 tained suspensions of fine particles and provided the variety of flow 

 rates used to control swimming speeds of fish, was used for this project. 

 A prototype respirometer (72-liter capacity), similar to that described 

 by Farmer and Beamish (1969), was also constructed (Sherk and O'Connor, 

 1971). The respirometer loop and centrifugal pump were type-316 stainless 

 steel. A cast acrylic chamber with plastic grids at each end was installed 

 in the lower section of the loop. An oval section cut from the top of the 

 chamber permitted insertion and removal of fish from the respirometer. 

 Rubber gaskets and hose clamps sealed the access port during experiments. 

 Straightening vanes upstream from the chamber ensured laminar flow. The 

 centrifugal pump was driven by a variable-speed electric motor. An orifice 

 plate in the upper part of the loop measured flow rates. Two needle valves 

 and a fill pipe on the upper side of the loop and two neoprene stoppered 

 openings in the chamber provided access to the water. These access points 

 were used extensively during experiments to bleed the respirometer of 

 trapped air, and to sample suspensions. At two points on the respirometer 

 loop, 20-meter copper coils controlled temperature via counter-current heat 

 exchange with water pumped from a constant temperature bath. 



Four inverted versions of the prototype respirometer (62-liter capacity) 

 were used for these experiments. Flow rates were measured by annular flow 

 sensors. A water jacket around the outside of the lower part of each loop 

 controlled temperature via counter-current heat exchange with water pumped 

 from a constant temperature bath. 



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