150-gram fish swimming at 1.58 £t/s in filtered river water were 10.8 

 and 55.3 mg O2 h"-"-, respectively (Fig. 15). Elevations of the lines 

 describing these data and hase-line data at 1.58 ft/s were different at 

 the 5-percent level (Table 17). 



c. Toadfish . Fish were held at least 5 days at 18° to 20° Celsius 

 and 5 parts per thousand salinity. Oxygen consumption rates were deter- 

 mined at a flow rate of 0.39 ft/s. Toadfish did not consistently swim into 

 the current. In filtered river water flowing at 0.39 ft/s, a 50-gram fish 

 used 5 mg O2 h"^ and a 150-gram fish used 10.1 mg O2 h"-^. Sex influence 

 on oxygen consumption rates was not apparent from these data (Table 18). 



Respiration rates of toadfish during exposure to 2.20 g 1"^ fuller's 

 earth were not different from rates determined under base-line conditions 

 (Table 19). During this exposure a 50-gram fish consumed 5.6 mg O2 h"-'^; 

 a 150-gram fish consumed 12.4 mg O2 h"-*-. Sex influence on respiration rates 

 was not apparent (Table 18). 



Oxygen consumption rates of toadfish during exposure to 1.58 g 1" 

 natural sediment were not different from base-line rates (Table 19). A 

 50-gram fish consumed 4.8 mg O2 h"-^; a 150-gram fish consumed 9.7 mg O2 h"-"- 

 in natural sediment suspensions. Male and female respiration rates during 

 exposure to 1.58 g 1~^ natural sediment differed in variance and elevation 

 at the 5-percent level (Table 18). 



Toadfish were held in 10.37 g I"''' natural sediment for 72 hours before 

 oxygen consumption rates were determined in filtered river water. These 

 rates were not different from base-line rates (Table 19). A 50-gram fish 

 used 2.2 mg O2 h~^; a 150-gram fish used 7.3 mg O2 h"^. A significant 

 difference was observed between the variances of respiration rates for 

 males and females during this experiment (Table 18) . 



Respiration rates were determined for toadfish in 3.36 g 1" natural 

 sediment after a 72-hour exposure to 11.09 g 1~ of the same material. 

 The variance associated with rates for fish in both the experimental and 

 base-line groups were different (Table 19). Oxygen consumption rates of 

 a 50- and 150-gram fish were 2.5 and 11.5 mg O2 h"^, respectively. Sex 

 influence on respiration rates was not apparent (Table 18) . Respiration 

 rates of toadfish exposed to natural sediment suspensions for 72 hours 

 were the same in filtered river water and in natural sediment suspensions 

 (Table 19). 



4. Discussion . 



Concentrations of suspended materials in an estuarine system are 

 highly variable. Storms, floods, tidal scour, or engineering activities 

 may increase concentrations of suspended particles. Naturally occurring 

 suspended loads exceeding 1 g 1"-^ are uncommon (Sherk, 1972). Masch and 

 Espey (1967) reported concentrations exceeding 10 g 1"-^ in dredge discharge 

 plumes and 100 g l"-"- in dredge-generated density flows. Suspended solids 

 concentrations used in this study typify those found near dredging opera- 

 tions. 



48 



