Glomerular filtration and urine flow in the euryhaline southern flounder, <i>Paralichthys lethostigma</i>, in seawater

Abstract

The glomerular filtration rate, determined with C-14 inulin, and urine flow rate were studied over a 10-month period in adult female southern flounder, Paralichthys lethostigma. The rate of glomerular filtration was low in winter, varying between 0.005 and 0.68 ml/h × kg body wt. (four fish), and higher in late spring, summer, and early fall, varying between 1.06 and 2.10 ml/h × kg (seven fish). The seasonal change in filtration rate corresponded to the migratory behavior of adults which migrate between a fully marine winter habitat on the continental shelf and a summer habitat in dilute, inshore waters. Urine flow rates varied between 0.11 and 0.85 ml/h × kg in different specimens, and was associated more closely with the solute load excreted than with the filtration rate. Both the glomerular filtration rate and the urine flow may fluctuate appreciably during an experiment.