Oxygen electrodes were calibrated and inserted through the fill pipes. 

 Time, temperature, dissolved oxygen concentration, and flow rate were 

 recorded for each respirometer as soon as it was set up and at hourly 

 intervals thereafter. Preliminary studies demonstrated that at a constant 

 flow of 0.28 ft/s, the hourly oxygen consumption decreased until the third 

 hour, after which rates were relatively constant. Data from the third hour 

 were used in all analyses. 



Several species were tested at various swimming speeds. The above 

 procedure was used until the third-hour data had been recorded. Flow rates 

 were then increased about 0.18 ft/s at 5-minute intervals until the desired 

 speed was achieved. The same parameters were recorded 5 minutes after 

 this speed was attained, and again 1 hour later. If information was re- 

 quired at higher levels of activity this procedure was repeated. All 

 parameters were monitored for 1 hour at each of the increased flow rates. 



At the end of each experiment the respirometers were drained and the 

 fish were removed for weighing, length measurement, and sex determination. 

 Respirometers were flushed with tapwater, then refilled with tapwater 

 until used again. Terramycin (oxytetracycline hydrochloride, 15-milligram 

 activity per liter) was added to the water when the respirometers would 

 not be used for longtime periods. 



Predetermined volumes of solids were added to about 16 liters of water 

 in 80-liter plastic trash cans. The slurries were aerated continuously, 

 and a submersible electric pump mixed the material. Slurries were prepared 

 18 hours before use, and were pumped into the respirometers as the units 

 were filled with holding tank water. Respirometers were washed several 

 times with tapwater at the end of experiments to prevent accumulation of 

 materials in the units. 



Concentrations of suspended materials were determined by the dry weight 

 difference between three 5-milliliter replicate samples drawn from each 

 respirometer at the beginning of an experiment, and three similar samples 

 drawn from the holding tank (no suspended material added) at the same time. 

 The oxygen demand of natural sediment suspensions was determined by measur- 

 ing the oxygen uptake of slurries. Slurries were pumped into the respirom- 

 eters as described above. Respirometers were set up as before but without 

 fish. Mean third-hour oxygen consumption values of the slurries were used 

 to check the oxygen demand of the sediment during experiments. 



The equipment used for long-term exposure of fish to suspensions of 

 solids is described in O'Connor, Neumann, and Sherk (1976) for bioassay 

 experiments or for sublethal hematological studies (see Section II). 



d. Data Analyses . Oxygen consumption rates were plotted against live 

 weight on double logarithmic grids. Curves were fitted to the data by 

 least squares linear regression analysis (Snedecor and Cochran, 1967) . 

 Correlation coefficients were determined for each group of data (Simpson, 

 Roe, and Lewontin, 1960) . 



