ABSTRACT
Improved estimates of urine flow rates of lampreys in various salinities were obtained by the collection of urine for periods of up to 48 h from minimally-stressed, unanaesthetized fish, following catheterization of the urinogenital papilla.
The mean urine flow rate of freshwater lampreys was 200·7 ± 14·3 ml kg−1 day−1.
Urine flow in freshwater lampreys was correlated with spontaneous changes in gill ventilation rate. MS222 anaesthesia reduced both ventilation and urine flow rates, but pronounced effects were only observed at concentrations greater than those needed to induce light anaesthesia (50–55 mgl−T). Urine flow rate in unanaesthetized fish was extremely sensitive to rapid (6°Ch−1) changes in temperature and Q10 (6–16°C) was approximately 5.
Urine flow rate decreased rapidly as the osmotic difference between the body fluids and environment approached zero, and the rate of flow in 30% seawater lampreys was only 7·6% that of freshwater fish.
There was no evidence for an effect of environmental calcium concentration on branchial osmotic permeability.
Extensive tubular reabsorption of ions occurred in freshwater lampreys. The total daily excretion rate of sodium ions generally decreased in salinities hyperosmotic to the plasma, indicating enhanced reabsorption, but secretion of magnesium and sulphate ions was greatly increased. Urine osmolarity was significantly increased in lampreys in hyperosmotic salinities.
Present data compare favourably with data obtained previously from anaesthetized animals, indicating that renal function in lampreys is not significantly impaired by light MS222 anaesthesia.
