THE METABOLISM OF RADIONUCLIDES BY MARINE ORGANISMS. I. THE UPTAKE, ACCUMULATION, AND LOSS OF STRONTIUM ⁸⁹ BY FISHES

¹ Hawaii Marine Laboratory, University of Hawaii, Honolulu 14, Hawaii

1. The ingestion of Sr⁸⁹ by large pelagic fishes results in the excretion of most of the isotope in a few hours. The small percentage remaining after one day persisted for the 27 days of the experiment. The strontium is rapidly eliminated from the visceral organs and tissues, but the structural tissues, including the bones, gills, integument and muscle, maintain their strontium level more or less constant. The turnover of strontium in these latter tissues is therefore slow.

2. Dark muscle, which has a better blood supply than light muscle, retains less Sr⁸⁹. Similarly, bone, which is better supplied with blood than is cartilage, retains less Sr⁸⁹ than the gill arches or the cartilaginous eye ossicles.

3. The excretion of Sr⁸⁹ by Tilapia mossambica is much slower than it is by the pelagic fishes. The percentage of the dose retained is somewhat larger, and most of the radioactivity is found in the structural tissues.

4. About three times as much Sr⁸⁹ was found in the muscle of an injected tuna as compared with another fish receiving the isotope orally. The gills of the former fish had only about half the activity found in the latter. From 60-70 per cent of the dose injected into Tilapia muscle was retained by these fish for 14 days. The long biological half-life of Sr⁸⁹ in fish muscle is contributing evidence for the slow turnover of muscle tissue in comparison with such tissues as liver or kidney.

5. Tilapia were able to concentrate Sr⁸⁹ directly from the sea water, although the ratio of Sr⁸⁹ in the fish to the Sr⁸⁹ in an equal weight of sea water was only about 0.3 after three weeks. Except for the visceral organs, the rank order of the retention of radioactivity in the various tissues is skeleton, integument, gills and muscle. This is the same distribution as was observed after oral administration of Sr⁸⁹. Because marine fish swallow water continually, a small amount of water in the gut might account for the relatively large percentage of radioactivity found in the viscera.