EXCRETION RENALE CHEZ UN POISSON EURYHALIN LE FLET (PLATICHTHYS FLESUS L) - CARACTERISTIQUES DE LURINE NORMALE EN EAU DOUCE ET EN EAU DE MER ET EFFECTS DES CHANGEMENTS DE MILIEU

The main features of the urinary function of the flounder (glomerular filtration rate or GFR, urine flow, osmotic pressure; Na, K, Cl, Ca concentration) are analyzed in fresh-water- and in sea-water-adapted animals. The evolution of these parameters is followed after transferring the fish from one medium into the other. The readjustment is complete after a period of about 48 hr. The kinetics concerning the GFR and the urine flow are different from those relative to the osmotic pressure and the electrolyte concentrations. The bladder urine differs significantly from the free-flow urine. This suggests a selective and slow reabsorptive function in the urinary bladder of the fish. "Laboratory diuresis" is not observed in the flounder. The "glomerular recruitment", that is varations of the number of the active glomeruli, is suggested to be a fundamental regulatory mechanism of the kidney function in this fish.