Table 11. --Mean Qio''" values for brine shrimp 

 nauplii at five salinities and five radia- 

 tion doses. Each value is the mean + 1 

 standard error for four replications. Q02 is 

 known to increase linearly in this tempera- 

 ture range 



Radiation 

 dose 



Rads 



1.98 

 +.03 



10,000 |l.9<; 



+ .03 



Salinity (p.p.t.) 



50 100 150 200 



-Qio- - 



20,000. 

 40,000. 

 80,000. 



1.98 

 + .01 



1.91 

 + .03 



1.9-4 

 + .02 



1.73 

 + .03 



1.54 

 ±.03 



1.46 

 ±.05 



1.32 

 + .01 



1.43 

 ±.06 



at 30° C. 



at 20 C. 



value are unknown. At 150 p.p.t. salinity, the 

 QjQ was lower for the control nauplii than for 

 irradiated nauplii and at 200 p.p.t. the Qjq for 

 the control group was greater than for the ir- 

 radiated groups. The Ojo values for unirradi- 

 ated nauplii were similar at salinities of 5,50, 

 and lOOp.p.t.butdecreasedat 150and ZOO p.p.t. 

 Differences were not significant among the 

 QlO values for nauplii that were irradiated with 

 10,000 or 20,000 rads and were in salinities of 

 50, 100, or 150 p.p.t. In a salinity of 5 p.p.t., 

 however, they had a higher Qjq and in a salinity 

 of 200 p.p.t. their Qjq was lower . The only dif- 

 ference between the Qjq values of nauplii that 

 were irradiated with either 40,000 or 80,000 

 rads (with the exception of the high Qjq at 

 80,000 rads and 100 p.p.t. salinity) was the 

 lower Q[Q at 200 p.p.t. 



Normal Respiration Rates for Brine Shrimp 

 Nauplii 



The relation we observed between respira- 

 tion rates of the unirradiated nauplii and sa- 

 linity (fig. 26) was different from those re- 

 ported by others. In one study, the respiration 

 rate of brine shrimp nauplii increased as 

 salinity descreased over a salinity range of 

 10 to 50 p.p.t. In the present study we noted 



the reverse--higher respiration rates at 50 

 p.p.t. than at 5 p.p.t. In another study no dif- 

 ference existed in Qq^ values of brine shrimp 

 nauplii in salinities np to about 100 p.p.t. It is 

 difficult to compare these data and ours be- 

 cause different methods and sonnetimes dif- 

 ferent strains of brine shrimp were used; how- 

 ever, the fact the salinity influences the met- 

 abolic rates of brine shrimp is well known. 



The effects of salinity on respiration are 

 usually reported as increased or decreased 

 respiration in salinities that are either sub- 

 normal or supernormal for the organism. On 

 this basis, respiration rates that were obtained 

 previously for brine shrin^p in different salini- 

 ties could not be compared with data from 

 other animals because the "normal" respira- 

 tion rate for brine shrimp had not been estab- 

 lished under conditions approaching those of 

 its environment. Thus, it was not possible to 

 know whether the measured Qq^ values re- 

 flected increases or decreases fr"om normal. 

 For our shrimp we assumed 200 p.p.t. is "nor- 

 mal," for they come from Great Salt Lake 

 where the salinity varies around 220 p.p.t. and 

 the ionic composition of the water is similar 

 to that of the water used in the present experi- 

 ment. Animals living in such an environment 

 for generations should be genetically adapted 

 to it. With reference to this "norm," all un- 

 irradiated animals at the lower salinities had 

 increased rates of respiration. Other investi- 

 gators have reported increased rates of res- 

 piration in subnormal salinities for other 

 crustaceans and suggested that the increased 

 metabolic rate of active animals held in sub- 

 normal salinities may be due to increased 

 random movement or to escape nnovements. 



The Site and Nature of Radiation Damage 



When the Qqt's of the irradiated nauplii 

 were compared as percentages of control 

 Qq2's, both stimulation and inhibition of res- 

 piration occurred under conditions that were 

 identical except for salinity (fig. 27). The res- 

 piration rates of nauplii irradiated with either 

 10,000; 20,000; or 40,000 rads appeared to de- 

 pend more upon the salinity of the water than 

 the amount of radiation received. Respiration 

 of the nauplii irradiated with these doses of 

 radiation was inhibited at 5 and 50 p.p.t. and 

 stimulated at 100 and 150 p.p.t. At 200 p.p.t. 

 salinity the respiration rate of the nauplii de- 

 creased with each increase in radiation dose 

 above 10,000 rads. Investigators using other 

 animals have observed stimulation of respira- 

 tion by low doses of radiation followed by 

 inhibition at higher levels, as we found at the 

 higher salinities (100 and 150 p.p.t.) and in- 

 hibition of respiration by all radiation doses, 

 as in nauplii at the lower salinities--5 and 

 50 p.p.t. 



From our data and those of others, it is 

 possible to speculate that radiation may lessen 



50 



