GO 



— . c_> 

 <=C UJ 



CD zn 



CO 



CD <_> 



95' 



72- 



CL. 



CD 



^8- 



END OF -^ 



EXPERIMENT^ 



96 HOURS 



PROBABLE 

 THRESHOLD 

 FOR ' 



gape response 

 190 mg/l-^I \ 



150 



200 



250 300 



Fig. 2. — Gaping response cur\-e. The 

 threshold concentration of potassium re- 

 quired to produce the gaping response 

 appears to be 190 mg/liter although a 

 longer exposure period than the 96 hours 

 used in our experiments would be neces- 

 sar\' to confirm the threshold. Clams ex- 

 posed to 458 mg of potassium per liter of 

 water did not gape, but clamped tightly 

 shut. 



POTASSIUn CONCENTRATION mg/l 



slope function was 1.5036 for the line used to derive the 

 96-hour LC50. In comparison with fish and snails, adult 

 Corbhula m. are sensitive to potassium. For example. 



the 96-hour LC50's for several test organisms exp)osed tc 

 potassium chloride, as reported in McKee & Wolf ( 1963 

 244), are: mosquitofish, Ganibusia affinis, 920 mg 



Fig. 3. — Corbicula manilensis under 

 potassium stress. The partially extended 

 foot is tightly clamped between the valvr< 

 and the foot has a puckered appearancr 

 The clam did not retract its foot in re 

 sponse to a flash of light or to handling. 



