SESSION IV 219 You have a built-in food supply and you can put the eggs in a chamber and expose them to a cobalt-60 source—expose thein for 90 to 100 days. At the end of the exposure period they are ready to start to feed; then you can take them out to the troughs. During the 90 to 100 days they have gone through their entire embryological development, They're fully formed little fish. WARREN: Lauren ought to also tell you that he has been studying . all of the abnormalities that can be produced in these fish with irradiation and that there's a certain mortality from this, depending upon ‘the dose rate. You get all of the abnormalities that have heen ascribed to this in other species and the large lethals are included in this list. But at this dose rate your abnormalities and your lethal effects are pretty low, aren't they? DONALDSON: There's no significant difference in the number of anomalies between the irradiated fish and the controls at the !evels we have used so far. FREMONT-SMITH: DONALDSON: TAYLOR: No increas<? Nosignificant increase. What is the LD-50 doze for a salmon? DONALDSON: Anacute dose is between 450 and 500 r. TAYLOR: You're giving them about 500 r, aren't you? DONALDSON: Chronic exposure. WARREN: Daily. DONALDSON: We'll give about 400 to 500 r this year, spread. over a 90- to 100-day period. AYRES: though. That's a time when cell reproduction is rather rapid, _ , DONALDSON: That's right. ee WARREN: At their maximum rate of growth and change. ably this should be the most sensitive period, shouldn't it? Presum-