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Urine production of the purple shore crab, hemigrapsus nudus Mathias, Diane Frances


Measurement of urine production by the crab, Hemigrapsus nudus, gives an indication of the excretion, in absolute amounts, of substances whose concentrations in the urine are presently known. In this way, it is possible to judge the degree of participation of the antennary glands in the functions of ionic and osmotic regulation. Urine production was measured, firstly, by blockage of nephropores to prevent urination and detection of resulting weight increases. The adhesive, methyl 2-cyano-acrylate monomer (M2C-2), provided a virtually perfect block against leakage by fusing the operculum to the surrounding exoskeleton. Secondly, the rate of inulin excretion following injection was employed for determination of urine production. Blockage with M2C-2 and inulin excretion gave urine production values of 15% to 17% body weight/24 hours in 2 5% salinity. With M2C-2 blockage, in 75% salinity, urine production was about 6% body weight/24 hours, however, inulin excretion indicated the rate in this salinity to be 12% body weight/24 hours. The M2C-2 values are believed to be the more reliable since they were more directly obtained and were replicated. It is evident, thus, that urine production increases with decrease in salinity. In both salinities, winter and summer crabs were used. Although seasonal differences in urine production were not entirely consistent, there is evidence to suggest that urine flow is greater in winter than in summer crabs in the low salinity. Urine production is independent of weight of crabs over the range sampled. It appears that urine production is proportional to the osmotic gradient existing between blood and the external salinity (blood is hypertonic to the salinities considered). Thus, seasonal and salinity effects on urine production presumably are related to changes in this osmotic gradient. It is hypothesized that the antennary glands function in this species for volume regulation by excreting excess osmotic water.

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