~L4but when goatfish and mullet are excluded the average is 53 per cent. Comparison of the Decline of Radioactivityby Species A comparison of the decline of radioactivity in two species with different feeding habits is made in Figures 3 and 4. Surgeonfish, with herbivorous habits, and grouper, with carnivorous habits, were selected as representing the conditions that probably prevailed in the fish in the vicinity of Belle Island. For comparisons of other species, reference may be made to Figures 7 through 10, which depict the decline in goatfish and mullet tissues. As has been pointed out, goatfish and mullet, because of their movement along the reef from island to island, are not strictly comparable to Belle Island "resident" fish, and the decline trends apparently reflect these differences. Surgeonfish and groupers were obtained fairly regularly throughout the period of investigation. The former feed prin- cipally on filamentous algae (Dawson, et al., 1955), whereas the groupers feed principally on fishes. The radioactivity in the surgeonfish, Figure 3, declines at a greater rate than that of the groupers, Figure 4, 100 days after the shot. for all tissues for the first 50 to For example, muscle tissue of surgeon- fish contained approximately four times as much radioactivity as that of the grouper immediately after the shot, but by 125 days the two species contained similar amounts. Comparison of the Decline of Radioactivity in Fish with that of their Food and with Other Factors In Figure 5 the radioactivity in surgeonfish viscera is