Whole animal transepithelial potential (TEP) of coho salmon during the parr-smolt transformation and effects of thyroxine,prolactin and hypophysectomy |
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| Authors: | Munehico Iwata Richard S Nishioka Howard A Bern |
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| Institution: | (1) Department of Zoology and Cancer Research Laboratory, University of California, Berkeley, CA 94720, USA;(2) Department of Zoology and Cancer Research Laboratory, University of California, Berkeley, CA 94720, USA;(3) Present address: Otsuchi Marine Research Center, OR1, University of Tokyo, Otsuchi, Iwate 028-11, Japan |
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| Abstract: | Whole animal transepithelial potentials (TEP) of yearling coho salmon (Oncorhynchus kisutch) in fresh water and after transfer to seawater were recorded throughout parr-smolt transformation (smoltification) from February to August 1984, along with plasma Na+ and Cl– concentrations and osmolality. Based on plasma ion regulation in seawater, the yearling coho in this study completed smoltification and attained sea-water adaptability in April. TEP in freshwater fish decreased (became inside-negative) after smoltification, and the TEP increased significantly (P < 0.01) after seawater transfer. When fish were transferred into seawater, thyroxine increased TEP of the transferred smolts by approximately 30% over the control level (P < 0.01) in April, but this did not occur when freshwater postsmolts were transferred in July and August. Hypophysectomy increased TEP (P < 0.01) in fresh water; it did not affect the TEP of the fish after seawater transfer. Ovine prolactin (3  g/g body weight) implanted into seawater-adapted fish caused a reduction in TEP (P < 0.01) when fish were exposed to fresh water. Whole-animal TEP appears to provide a valuable index of the completion of smoltification (April–May) and a useful tool for investigating the endocrine control of salmonid osmoregulation. |
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| Keywords: | transepithelial potential whole animal smoltification osmoregulation hypophysectomy teleost seawater adaptation salmonid |
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