Printed in Great Britain WATER-ELECTROLYTE BALANCE IN GOLDFISH CARASSIUS AURATUS, UNDER CONSTANT AND DIURNALLY CYCLING TEMPERATURE CONDITIONS

1. The effects of acclimation to constant and diurnally cycling tempera-tures upon water-electrolyte regulation were examined in goldfish held at 20, 25, 30 and 25 + 5 °C, and sampled at 03.00, 09.00, 15.00 and 21.00 h. Plasma and epaxial muscle levels of Na, K, Ca, Mg, Cl and water were determined. Using Cl space as an indicator of extracellular phase volume, mean cellular cation concentrations were estimated. 2. Fish held at constant temperature exhibited significant diurnal variations in all ions except plasma magnesium and muscle potassium. With the exception of muscle choride, however, the occurrence of peak and/or minimum concentrations tended to be inconsistent in relation to specific sampling times. Somewhat more regularity was apparent in terms of dark or light periods. 3. Under constant temperature conditions plasma Cl increased with in-creasing temperature, while Na declined. Plasma magnesium was con-sistently higher at 25 °C than at either 20 or 30 °C. This was true of muscl