lab21 - J. Exp. Biol. (1969), 50, 179-190 With 1...

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J. Exp. Biol. (1969), 50, 179-190 With 1 text-figure Printed in Great Britain SODIUM, CHLORIDE AND WATER BALANCE OF THE INTERTIDAL TELEOST, PHOLIS GUNNELLUS BY DAVID H. EVANS* Department of Biological Sciences, University of Lancaster, Lancaster, England (Received 18 June 1968) INTRODUCTION Studies of the sodium, chloride and water balance of Xiphister atropurpureus (Evans, 1967 a-c) 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, Pholis gunnellus, 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 Specimens of Pholis gunnellus 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 Gammarus sp. or Nereis 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 by Pholis, 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 ( M Na or M 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.
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180 DAVID H. EVANS (9 days), washing in non-radioactive medium for approximately 2 min. and then monitoring the decrease in radioactivity in the fish (using the whole-body counter) for 48 hr. The efflux of sodium from fish injected intraperitoneally with the isotope
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lab21 - J. Exp. Biol. (1969), 50, 179-190 With 1...

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