84 



Atomic Radiation and Oceanography and Fisheries 



to a very fine state. Plutei of the sea urchin, 

 Arbacia piinctnlata were put into sea water con- 

 taining the radioruthenium which was kept in 

 suspension by aerating the culture flask. After 

 18 hours, the larvae were rinsed and resus- 

 pended in fresh sea water. Aliquots of larvae 

 were then removed at intervals and tested for 

 radioactivity (Table 5). A microscopic ex- 



TABLE 5 The Decrease of Ru^°* in Sea Urchin 



Larvae as a Function of Time in 



non-radioactive water 



Radioactivity in 500 

 Hours larvae (counts/minute) 



1 1413 



4 179 



8 148 



amination of the larvae at zero time showed that 

 the intestines were filled with the radioactive 

 particulate material, but at 8 hours, very little 

 material was left in the gut. Apparently little 

 ruthenium was actually absorbed through the 

 digestive tract. 



The ingestion of the particulate (co-precipi- 

 tated) ruthenium by the bay scallop, Pecten 

 irradians, also indicated that the radioactivity 

 was mostly associated with the digestive tract. 

 The crystalline style was highly radioactive, al- 

 though the radioactivity in it decreased during 

 the five days the scallops were kept in running 

 water. The hepatopancreas, on the other hand, 

 showed an increase in radioactivity during this 

 time. No radioactivity was found associated 

 with the internal organs other than those in the 

 digestive tract. 



Third trophic level 



The uptake, accumulation, and loss of radio- 

 nuclides has been studied in many fishes by 

 both the R.L.F.W.S. and the H.M.L. These 

 fishes include the skipjack tuna {Eiithynnus 

 yaito), yellowfin tuna {Neothnnntts macrop- 

 terus), dolphin {Coryphaena hip punts'), papio 

 {Carangoides ajax), aholehole (Kuhlia sand- 

 vicensis) , Tilapia mozamhique , menhaden {Bre- 

 voortia tyratinus), bluefish {Pomatomus salta- 

 trix) , little tuna (Euthynnus allitteratus) , croak- 

 ers (Micropogon undulatus) , and king whiting 

 {Menticirrhus sp.) . 



At the H.M.L., strontium^^ in gelatine cap- 

 sules was fed to skipjack, dolphin, and yellowfin 

 tuna. These are all fast-swimming pelagic fish. 

 Figure 6 shows that the excretion of strontium 



is very rapid. In 24 hours, only about two per 

 cent of the dose remains in the fish. Similar ex- 

 periments with Tilapia, a small, sluggish bottom 

 feeder, indicate that the strontium is also mainly 

 excreted, but that the time required to reach a 

 minimum level of about five per cent of the 

 dose requires at least four days. This informa- 

 tion is consistent with the idea that the meta- 

 bolic rates of these fishes are very much dif- 

 ferent, and the sluggish fish might be expected 

 to retain the strontium for longer periods. 



HOURS AFTER DOSE 



Figure 6. 



The Percentage Accumulation by Tuna 

 Fish of Sr'" Given Orally. 



The internal distribution of the total radio- 

 activity recovered is shown in Table 6. By 

 plotting the radioactivity of each organ against 

 time, it is apparent that the soft, visceral tissues 

 rapidly excrete the strontium, but that the bony 

 structures, gills, integument, and muscles re- 

 tain the strontium for a long period. Tilapia 

 show the same behavior. The data are presented 

 in Table 7. 



The direct uptake of strontium*^ in solution 

 by Tilapia was also studied at the H.M.L. Fig- 

 ure 7 shows that after about two weeks, the 



Figure 7. The Uptake of Sr^" in Solution by 

 Tilapia Mozambique. 



