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EFFECT OF ABRUPT CHANGE IN THE SALINITY OF THE ENVIRONMENT ON PLASMA ELECTROLYTES, URINE VOLUME, AND ELECTROLYTE EXCRETION IN CHANNEL CATFISH, ZCTALURUS PUNCTATUS VIRGINIA M. NORTON AND KENNETH B. DAVIS Department of Biology. Memphis State University. Memphis. TN 38152. USA (Rewired 19 Ma!, 1976) Abstract- --I. Plasma Na levels of fish transferred from fresh water to salt water remained hypernatremic to the environment; however, plasma Cl remained at or near the environmental level. 2. Acclimation in salt water hyperionic to plasma ions required I5 days; in a medium isonatremic and hyperchloremic acclimation required 3 days, but in isoionic medium no change in plasma ions occurred. 3. Handling did not affect plasma Na and Cl of fresh water fish. 4. Acclimation in isoionic salt water had no effect on the response of plasma electrolytes to a hypcrionic medium. 5. Plasma Na and Cl decreased significantly after transfer from salt to fresh water. 6. Fish in salt water produced small amounts of concentrated urine hypoosmotic to the plasma. compared to the large volume of dilute urine produced by fish in fresh water. INTRODUCTION Most literature on hydromineral balance in teleosts is concerned with a few euryhaline species. particu- larly Furrdulus and migrating species such as catadro- mous eels and anadromous salmon (Black. 1957; Parry, 1966; Holmes & Donaldson, 1969; Hickman & Trump, 1969; Bentley, 1971; Johnson, 1973; Grif- fith, 1974). Euryhaline fish generally regulate body osmolality within rather narrow limits regardless of the external environment, but stenohaline fish are affected by osmotic fluctuations and can survive small variances in the medium by tolerating changes in their body fluid concentration. The commonly studied euryhaline species are pri- marily cold water animals. Information on warm water stenohaline fresh water (FW) species is meager. The channel catfish, Ictulurus punctatus, is a warm water stenohaline FW fish and has been found in brackish water in Louisiana (Perry, 1967; Perry & Avault. 1968). The upper limit for survival was found to be 11.0 g/l. dilute sea water (Allen & Avault, 1971). Osmoregulation has been studied in two Ictalurids, I. rrehulosus (Walker, 1971) and hypophysectomized I. rtrrlcls (Chidambaram. 1972). The specific mechanisms involved in acclimation of a stenohaline FW fish to change in environmental salinity are not clearly understood. This paper examines the effects of handling stress. and abrupt change in osmotic con- centration of the environment on plasma ion regula- tion and renal adjustments in channel catfish. MATERIALS AND METHODS Cultured juvenile catfish were obtained from the Fish Farming Experimental Station. Stuttgart, AR, and main- tained in indoor FW recirculating raceways. During accli- mation. fish were exposed to a natural photoperiod and temperatures of 2&30 C. Experiments involving transfer from FW to salt water (SW), or SW to FW, were con- ducted in recirculating raceways which utilized biofilters (Parker & Simco, 1973). The raceway used for SW exper- iments consisted of two 1700 I. circular, aluminum tanks connected to a 1700 I. oblong filter box.
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This note was uploaded on 09/12/2010 for the course BIOLOGY 225 taught by Professor Pavgi during the Winter '10 term at University of Michigan.

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