only a few studies have considered the inter- 

 acting effect of the two factors. The ability of 

 irradiated and unirradiated juveniles of the 

 silver salmon to migrate from fresh water to 

 the sea was affected by the interactionof radi- 

 ation and salinity. Radiation and salinity also 

 interacted to affect the survival of: the mummi- 

 chog; the grass shrimp; the brine shrimp; and 

 the rainbow trout, Salmo gairdneri. The loss of 

 sodium 12. by the mummichog also was affected 

 by the interaction of radiation and salinity. 



We examined the effects of salinity, radi- 

 ation, and their interaction on metabolism of 

 1-day-old nauplii of the brine shrimp. Brine 

 shrimp were chosen because they naturally 

 tolerate a very wide range of salinities and 

 are relatively resistant to radiation. The early 

 nauplius stage was used to minimize differ- 

 ences in respiration rates due to size and stage 

 of development. The effect of radiation and 

 salinity on the brine shrimp was measured by 

 changes in the respiratory metabolisnn (both 

 Qq and Qin) of the nauplii. 



Experimental Procedures 



Brine shrimp from Great Salt Lake, Utah, 

 which has a salinity of 220 p.p.t., were used 

 throughout the experiments. Nauplii were 

 hatched in 30 p.p.t. sea water at room tem- 

 perature (22° C.) and transferred soon after 

 hatching to one of five salinities--5, 50, 100, 

 150, or 200 p.p.t. All sea-water solutions were 

 made from an artificial sea-salt mixture. 

 After overnight acclimation to the desired 

 salinity, the 1-day-old nauplii were exposed to 

 doses of 10,000; 20,000; 40,000; or 80,000 rads 

 of cobalt 60 radiation. Radiation was adminis- 

 tered at a rate of 365 rads/min. ilO percent 

 at room temperature and with continuous aera- 

 tion. Controls were treated similarly except 

 for irradiation. 



Respiration was measured during the first 

 4 hours after irradiation on a differential 

 respirometer. Each flask contained the ani- 

 mals present in 3 ml. of water taken from 

 a dense population of nauplii plus 0.5 ml. of 

 20 percent KOH in the side arm. During res- 

 piration determinations the flasks were shaken 

 80 times per minute and maintained at 20° C. 

 Respiration rates, Q02 values, were calculated 

 as //1.02/mg. dry weight/hour. Respiration 

 rates at temperatures of 20° and 30° C. were 

 used to obtain Qjq values. The Qjq values 

 were calculated without using Qq„ values for 

 any intermediate temperatures because res- 

 piration rates of brine shrimp nauplii have a 

 linear relation to temperature between 20 and 

 30° C. Analyses of variance were calculated 

 to determine the significance of the main ef- 

 fects and interaction of radiation and salinity 

 on Qq and Q.^values. Duncan's multiple 

 rangeTest was used to test for significant dif- 

 ferences between mean values. In the follow- 



ing text all reported changes or differences 

 between Qq^'s orQ^Q'satdifferent combina- 

 tions of salinity and radiation dose are statis- 

 tically significant at the 5-percent probability 

 level or less. 



Effect of Salinity and Radiation on 

 Respiration Rates 



Measurements of respiration rates (Q02) 

 at 20° C. show that salinity affected the respira- 

 tion rates of both control and irradiated brine 

 shrimp nauplii (fig. 26), Mean Qq. values 

 within the controls and within each irradiated 

 group were higher at 50 p.p.t, salinity than at 

 5 p.p.t., and were lowest at 200 p.p.t., the sa- 

 linity nearest that of their natural habitat. 

 Respiration rates for the control group de- 

 creased progressively with each increase in 

 salinity from 50 to 200 p.p.t., whereas respira- 

 tion rates for each group of irradiated nauplii 

 were nearly constant at salinities of 50 to 

 150 p.p.t. The apparently low Qq for animals 

 that received 80,000 rads and were in 100 p.p.t. 

 salinity was not significantly different from 

 the Qq„ of nauplii that received the same dose 

 and were in 5 p.p.t. salinity. 



Analysis of variance proved that radiation 

 and the salinity-radiation interaction also af- 

 fected the respiration rates of brine shrimp. 

 The effect of radiation was most apparent at 

 80,000 rads, at which dose the rate of respira- 

 tion of irradiated nauplii decreased in all sa- 

 linities. The effect of the interaction between 

 salinity and radiation was also shown by the 

 mean Qq, values. All irradiated nauplii at the 

 lowest salinity, 5 p.p.t., and those irradiated 

 with 40,000 or 80,000 rads in the highest sa- 

 linity, 200 p.p.t., respired more slowly than 

 the controls. Nauplii irradiated with 10,000; 

 20,000; and 40,000 rads in 150 p.p.t., and those 

 irradiated with 20,000 and 40,000 rads in 

 100 p.p.t. respired more rapidly than the con- 

 trols. Nauplii with the lowest respiration rates 

 (those irradiated with 40,000 and 80,000 rads 

 at 200 p.p.t.) died within 24 hours after irradi- 

 ation. 



Effects of Radiation and Salinity on 

 Qjq Values 



Most of the mean Qjq values for unirradiated 

 and irradiated brine shrimp nauplii for the 

 temperature range of 20° to 30° C. were near 

 what might be expected of a thermobiologic 

 reaction (table 11). An analysis of variance, 

 however, showed that salinity and the salinity- 

 radiation interaction affected the Qjq much 

 more than did radiation itself. At salinities of 

 5, 50, or 100 p.p.t. the mean Qjq values for 

 controls or any irradiated group did not differ 

 except the group irradiated with 80,000 rads 

 at 100 p.p.t. This Qjq. larger than all others, 

 was reproducible, but reasons for the high 



48 



