Effects of rapid changes in salinity on the renal function of a euryhaline teleost

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Abstract
Techniques developed to study renal function of the euryhaline teleost, Fundulus kansae, are described. Effects of a sudden transfer from fresh water to sea water on urine flow and urine and serum osmotic pressures were studied. Glomerular filtration rates (GFR) of animals adapted to fresh water and to sea water for 7 days were estimated. Urine flow was found to be a function of size and of handling, as well as of salinity. Animals held in fresh water showed an initial diuresis which reached a peak approximately 2 hr after cannulation. Urine flow thereafter was in the range of 200 ml/kg per day for fish weighing 1.58 ± 0.3 g, and the estimated GFR was 600 ml/kg per day. Animals held in sea water had urine flows ranging from 5 to 20 ml/kg per day, and filtration rates ranging from 20 to 45 ml/kg per day were estimated. The urine collected from the 2nd to approximately the 10th day after a sudden transfer into sea water was hypertonic to the serum. It is concluded that both a reduction in GFR and an increase in the tubular reabsorption of water are elements of renal function utilized when this animal moves from a hypotonic to a hypertonic environment.

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