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Water, sediments, and zooplankton from unproductive Fern Lake were compared with those from highly productive Bay Lake and with data from the literature. In all cases, values from the Fern Lake system were in the lower or lowest range of conductance and concentration values. Consistently higher values were found in the Bay Lake samples. These differences may account partially for the productivity differential between Bay and Fern Lakes, but a major factor may be the difference in the flushing or the retention time of the lakes, as determined by the ratio of total precipitation on the watershed to lake volume. This ratio has been estimated as 26 for Fern Lake and 4.8 for Bay Lake.

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FISH PHYSIOLOGISTS AND NUTRI-TIONISTS frequently study the transport rates of substances introduced into the digestive systems of fish. If the studies are to be quantitative, it is necessary to know the exact amounts introduced. The most common procedure is to enclose the substance in a gelatin capsule and forcefeed it to the fish with a suitable insertion tool. This procedure has been used for studies of chemical toxicity (Loeb, 1960)0 radiation damage (Nakatani, 1962), and isotope uptake (Martin and Goldberg, 1962).In our studies, we attempted to make quantitative measurements of the absorption rates of certain trace elements which were introduced with a normal diet to small fingerling trout and salmon. We found that gelatin capsules were not suitable for this purpose: even the smallest capsules were too large for small fingerlings (fork length, 80 to 100 millimeters). In addition, all the contents might not be released, owing to incomplete breakdown of the gelatin in the upper digestive tract. These problems were averted by using a food pellet of suitable size and uniform content.

SUMMARY The gross chemical composition of the Rongelapese diet indicates that it is low in fat, protein, and ash hut fairly high in carbohydrate. The variation in gross chemical composition of the diets examined may be accounted for by the broad variability of the different diets. The habitat of the Rongelapese probably does not demand a high‐energy diet, which may partially justify the lower fat intake. Levels of calcium and phosphorus seem below the minimum required for maintenance of a proper calcium‐phosphorus balance. The diet seems adequate in magnesium and potassium but slightly low in sodium. The nickel, cobalt, and copper contents seem high in the Rongelap rations, manganese content is low, and iron and zinc compare favorably with minimum daily requirements. Hight levels of cobalt‐60 and zinc‐65 are associated with each other and with rations containing local fish. The higher levels of strontium‐90 and cesium‐137 are found where local fruit was consumed. Coconut contributes little strontium‐90, and pandanus the most. Rations with higher zinc‐65 also contain higher levels of stable zinc, indicating that local sea foods may be the main source of zinc in the diet. Cesium‐137, strontium‐90, and cobalt‐60 show no definite correlation with stable potassium, calcium, and cobalt, respectively. There is probably a net addition of minerals to Rongelap soils from imported foods.