in the contents of the digestive tract accounted for most of the radioactivity found in the invertebrates. amount, however, was absorbed into the tissues. An appreciable Muscle con- sistently had the lowest specific activity and digestive tract with its content the highest. Other tissues or organs varied in ranking depending on the species. In general invertebrates taken at the northern stations were the most radioactive. The decrease in radioactivity from north to south appeared to be more rapid on the east than on the west side of the lagoon. 4.5 Fish Materials and Methods. The fish specimens were collected in water poisoned with derris root powder in depths up to 12 feet, usually on the lagoon side of each of the station islands. Areas selected for poisoning had a minimum of current combined with adequate coral and substrate to support the typical reef population of fishes. The number of fish collected waried from 26 to over 300 per station depending on the success of the poisoning opera~ tion and the number of species present. These fish represented from 10 to over 30 families and varied in weight from less than a gram to 1,589 grams (average 51.1 grams). Although there were several hundred species of fish living on the reef, the species selected for analysis of padio- — activity were those most common to all stations and those that were representative of the various types of feeding habits. - b3 -