lab19 - Corn#. Bioehem. Physiol., 1969, Vol. 28, p p. 1427...

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Corn#. Bioehem. Physiol., 1969, Vol. 28, pp. 1427 to 1433. Pergamon Press. Printed in Great Britain SODIUM EXCHANGES IN GOLDFISH (CARASSIUS AURATUS L.) ADAPTED TO A HYPERTONIC SALINE SOLUTION* BRAHIM LAHLOU,t I. W. HENDERSON~ and W. H. SAWYER Department of Pharmacology, College of Physicians and Surgeons, Columbia University, New York, New York (Received 5 August 1968) Abstract--1. Goldfish were adapted to diluted sea water (190 m-equiv./1 of Na) which was hyperosmotic to plasma from fresh-water-adapted fish. Fish survive well in this medium but plasma Na levels rise to equal those of the environment and exchangeable Na increases by 74 per cent. 2. Fish in this hyperosmotic medium increase Na outflux about twenty times. They also increase their Na influx and drinking rates and decrease free-water excretion. 3. Despite such adjustments, goldfish do not osmoregulate effectively. The goldfish appears to be stenohaline chiefly because it lacks the ability to excrete enough Na actively across the gills to balance the increased Na intake from the hyperosmotic environment. INTRODUCTION STENOHALINE fishes, either fresh water or marine, maintain the constancy of their internal fluids only when the salinity of the environment remains within a limited range. Their osmoregulatory mechanisms cannot cope with rapid or wide fluctuations in external salinity. The goldfish is a stenohaline fresh-water fish. If transferred directly to sea water it dies within about ½ hr. If similarly transferred to half-strength sea water it dies in 2 or 3 hr. In these circumstances there is rapid weight loss and rapid influx of salts, resulting in a dramatic increase in plasma electrolyte concentrations (unpublished observations). If adapted gradually, however, goldfish have been reported by Pora (1939) to survive indefinitely in half-strength sea water. In this paper we have attempted to find out how this stenohaline fresh-water fish adapts to a hyperosmotic environment and how its means of adaptation differ from those of a truly euryhaline fish. * Supported in part by Grant AM-01940 from the National Institute of Arthritis and Metabolic Diseases, and a General Research Support Grant from the National Institutes of Health. t Aided by travel grants from Minist~re des Affaires Etrang~res (Paris) and from Commissariat G6n6ral du Plan d'Equipement et de la Productivit6 (Paris). Present address : Groupe de Biologie marine du CEA, Station Zoologique, 06-Villefranche-sur-mer, France. ~: Harkness Fellow of the Commonwealth Fund, 1966-68. Present address: Department of Zoology, The University, Sheffield, England. 1427
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1428 BRAHIM LAHLOU, I. W. HENDERSON and W. H. SAWrSa MATERIALS AND METHODS Goldfish, weighing 15-80 g, were adapted to diluted artificial sea water (Instant Ocean Sea Salts, Aquarium Systems, Inc.) in two steps. They were first placed for several days in a solution approximately isosmotic to plasma (Na concentration of 140 m-equiv./l) and then transferred to a defirfitely hypertonic medium (Na = 190 m-equiv./l). The fish survive well and eat normally in this environment. The only evident change was pronounced melanization in some fish. This indicates that high salinity produces some endocrine
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lab19 - Corn#. Bioehem. Physiol., 1969, Vol. 28, p p. 1427...

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