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      Mechanisms of seawater acclimation in a primitive, anadromous fish, the green sturgeon

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          Abstract

          Relatively little is known about salinity acclimation in the primitive groups of fishes. To test whether physiological preparative changes occur and to investigate the mechanisms of salinity acclimation, anadromous green sturgeon, Acipenser medirostris (Chondrostei) of three different ages (100, 170, and 533 dph) were acclimated for 7 weeks to three different salinities (<3, 10, and 33 ppt). Gill, kidney, pyloric caeca, and spiral intestine tissues were assayed for Na +, K +-ATPase activity; and gills were analyzed for mitochondria-rich cell (MRC) size, abundance, localization and Na +, K +-ATPase content. Kidneys were analyzed for Na +, K +-ATPase localization and the gastro-intestinal tract (GIT) was assessed for changes in ion and base content. Na +, K +-ATPase activities increased in the gills and decreased in the kidneys with increasing salinity. Gill MRCs increased in size and decreased in relative abundance with fish size/age. Gill MRC Na +, K +-ATPase content (e.g., ion-pumping capacity) was proportional to MRC size, indicating greater abilities to regulate ions with size/age. Developmental/ontogenetic changes were seen in the rapid increases in gill MRC size and lamellar length between 100 and 170 dph. Na +, K +-ATPase activities increased fourfold in the pyloric caeca in 33 ppt, presumably due to increased salt and water absorption as indicated by GIT fluids, solids, and ion concentrations. In contrast to teleosts, a greater proportion of base (HCO 3 and 2CO 3 2−) was found in intestinal precipitates than fluids. Green sturgeon osmo- and ionoregulate with similar mechanisms to more-derived teleosts, indicating the importance of these mechanisms during the evolution of fishes, although salinity acclimation may be more dependent on body size.

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          The multifunctional fish gill: dominant site of gas exchange, osmoregulation, acid-base regulation, and excretion of nitrogenous waste.

          The fish gill is a multipurpose organ that, in addition to providing for aquatic gas exchange, plays dominant roles in osmotic and ionic regulation, acid-base regulation, and excretion of nitrogenous wastes. Thus, despite the fact that all fish groups have functional kidneys, the gill epithelium is the site of many processes that are mediated by renal epithelia in terrestrial vertebrates. Indeed, many of the pathways that mediate these processes in mammalian renal epithelial are expressed in the gill, and many of the extrinsic and intrinsic modulators of these processes are also found in fish endocrine tissues and the gill itself. The basic patterns of gill physiology were outlined over a half century ago, but modern immunological and molecular techniques are bringing new insights into this complicated system. Nevertheless, substantial questions about the evolution of these mechanisms and control remain.
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            Methods for Nonlethal Gill Biopsy and Measurement of Na+, K+-ATPase Activity

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              The parr—Smolt transformation (smoltification) and seawater adaptation in salmonids

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                Author and article information

                Contributors
                pallen@cfr.msstate.edu
                Journal
                J Comp Physiol B
                Journal of Comparative Physiology. B, Biochemical, Systemic, and Environmental Physiology
                Springer-Verlag (Berlin/Heidelberg )
                0174-1578
                1432-136X
                11 June 2009
                October 2009
                : 179
                : 7
                : 903-920
                Affiliations
                [1 ]Department of Wildlife, Fish, and Conservation Biology, University of California, 1 Shields Avenue, Davis, CA 95616 USA
                [2 ]Department of Animal Science, University of California, 1 Shields Avenue, Davis, CA 95616 USA
                Author notes

                Communicated by G. Heldmaier.

                Article
                372
                10.1007/s00360-009-0372-2
                2745624
                19517116
                0db001a0-5172-4e8c-b984-51b95d35743d
                © The Author(s) 2009
                History
                : 23 March 2009
                : 21 May 2009
                : 22 May 2009
                Categories
                Original Paper
                Custom metadata
                © Springer-Verlag 2009

                Anatomy & Physiology
                acipenser medirostris,na+, k+-atpase,mitochondria rich cell,cl−/hco3− exchange,green sturgeon,pyloric caeca

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