J. Exp. Biol.
(1969), 50, 179-190
Printed in Great Britain
SODIUM, CHLORIDE AND WATER BALANCE OF THE
BY DAVID H. EVANS*
Department of Biological Sciences, University of Lancaster,
Studies of the sodium, chloride and water balance of
showed that this intertidal teleost is relatively impermeable to these ions and
to water, has an exchange-diffusion system for sodium only, and apparently lowers its
permeability to sodium but not to chloride or water when acclimated to a lower
salinity. An investigation of the intertidal teleost,
was undertaken to
determine whether the sodium, chloride and water balance of this species exhibit the
same characteristics and to explore further the problem of the sodium, chloride and
water balance of teleosts in general.
MATERIALS AND METHODS
were collected at Menai Bridge, Anglesey, Wales.
Individuals weighed from 1 to 12 g. and were kept in 10 1. Perspex aquaria in a
constant-temperature room (10+ i° C.) in which most experiments were performed.
Fish were fed
sp. only if kept in the laboratory longer than
2 weeks. 100% sea water contained 410 mM-Na/1. and was made up by adding
quantities of a sea-salt mixture (Pantin, 1959) to dilute sea water obtained from
Morecambe Bay. It was observed that 20 % sea water was the lowest salinity tolerated
and animals were acclimated to this salinity for at least 5 days before experi-
ments were performed. Weighings of individual fish were performed on a Mettler
balance to 0-05 g. after drying with paper towelling; MS 222 (o-oi %) was used for
anaesthetization. Experiments were performed without regard to sex or reproductive
state. All experimental values are expressed as mean + S.E. (number of samples).
The influx of sodium (
Na) was studied by loading fish in a radioactive bath
of 100—200 ml. of either 100% or 20% sea water containing approximately 1 /iC./ml.
of radio-sodium. After 1 hr. the fish were removed and washed for from 2 to 3 min.
The amount of radioactivity in the fish and in samples of the medium was determined
using a Nuclear Enterprises whole-body counter. In some experiments the efflux of
sodium was followed by placing fish that had been loaded in this way (for 1 hr.) into
100 ml. of the desired salinity and counting the radioactivity in the fish and in the
medium after 1 hr. The ' compartmentalization' of the sodium efflux from fish
acclimated to 100% sea water was studied by loading four fish to isotopic equilibrium
• Present address: Department of Biology, University of Miami, Coral Gables, Florida 33124, U.S.A.