overflowed into reservoir 3. Both the constant level chamber and 

 distribution chambers served to maintain constant flow rates into 

 the respiratory chambers. The flow rates out of the respiratory 

 chambers were regulated by 20-gauge hypodermic needles. From the 

 chambers the salinity medium entered reservoir 3. The needles were 

 fixed to a flow control board at the same level. Flow rates can be 

 altered by changing the level of the control board or by changing 

 the gauge of the needles. 



Disposable syringe bodies (10 ml) containing a small amount of 

 filter material (Metaframe Spic and Spun balls) were placed in the 

 line before the hypodermic needles. The filter material trapped the 

 particulate matter coming out of the respiratory chambers and was 

 replaced daily. The untrapped material may block the needles, oc- 

 casionally resulting in the death of some test animals. 



The dissolved oxygen levels were determined by diverting the 

 flow from the respiratory chambers to the oxygen probe chamber by 

 means of a 3-way stopcock. The stopcock was installed between the 

 syringe body and the needle. Reservoir 3 received water from the 

 constant level chamber, respiratory chambers, and/or probe chamber. 

 This water was periodically returned to the respective reservoir 

 (either R, or R^) through a small pump operated by a magnetic relay 

 switch. 



The volume of the respiratory chambers was adjusted to about 

 400 ml and the flow rates to 800 ml per hour. These rates were 

 established on the basis of the size of the test shrimp. In de- 

 termining the flow rates, care was taken to maintain the dissolved 

 oxygen levels in the respiratory chambers well above the critical 

 levels. At room temperature (circa 25°C) the level is in the vi- 

 cinity of 2.0 ml O^/L. It is higher at 32°C. At 18°C the O2 satu- 

 ration is always maintained at higher levels than the actual con- 

 sumption. 



44 



