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      The physiology of the Tambaqui (Colossoma macropomum) at pH 8.0.

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          Abstract

          The Tambaqui is a model neotropical teleost which is of great economic and cultural importance in artisanal fisheries and commercial aquaculture. It thrives in ion-poor, often acidic Amazonian waters and exhibits excellent regulation of physiology down to water pH 4.0. Curiously, however, it is reported to perform poorly in aquaculture at pH 8.0, an only slightly alkaline pH which would be benign for most freshwater fish. In initial experiments with Tambaqui of intermediate size (30-50 g), we found that ammonia excretion rate was unchanged at pH 4, 5, 6, and 7, but elevated after 20-24 h at pH 8, exactly opposite the pattern seen in most teleosts. Subsequent experiments with large Tambaqui (150-300 g) demonstrated that only ammonia, and not urea excretion was increased at pH 8.0, and that the elevation was proportional to a general increase in MO2. There was an accompanying elevation in net acidic equivalent excretion and/or basic equivalent uptake which occurred mainly at the gills. Net Na+ balance was little affected while Cl- balance became negative, implicating a disturbance of Cl- versus base exchange rather than Na+ versus acid exchange. Arterial blood pH increased by 0.2 units at pH 8.0, reflecting combined metabolic and respiratory alkaloses. Most parameters recovered to control levels by 18-24 h after return to pH 6.0. With respect to large Tambaqui, we conclude that a physiology adapted to acidic pH performs inappropriately at moderately alkaline pH. In small Tambaqui (4-15 g), the responses were very different, with an initial inhibition of ammonia excretion rate at pH 8.0 followed by a subsequent restoration of control levels. Elevated ammonia excretion rate occurred only after return to pH 6.0. Furthermore, MO2, plasma cortisol, and branchial vH+ATPase activities all declined during pH 8.0 exposure in small Tambaqui, in contrast to the responses in larger fish. Overall, small Tambaqui appear to cope better at pH 8.0, a difference that may correlate with their natural history in the wild.

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          Author and article information

          Journal
          J Comp Physiol B
          Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology
          Springer Science and Business Media LLC
          1432-136X
          0174-1578
          May 2018
          : 188
          : 3
          Affiliations
          [1 ] Department of Zoology, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada. woodcm@zoology.ubc.ca.
          [2 ] Department of Biology, McMaster University, Hamilton, ON, Canada. woodcm@zoology.ubc.ca.
          [3 ] Rosenstiel School of Marine and Atmospheric Science, University of Miami, Florida, USA. woodcm@zoology.ubc.ca.
          [4 ] Laboratory of Ecophysiology and Molecular Evolution, Brazilian National Institute for Research of the Amazon (INPA), Manaus, Amazonas, Brazil. woodcm@zoology.ubc.ca.
          [5 ] Department of Biology, University of San Diego, San Diego, CA, USA.
          [6 ] Laboratory of Ecophysiology and Molecular Evolution, Brazilian National Institute for Research of the Amazon (INPA), Manaus, Amazonas, Brazil.
          Article
          10.1007/s00360-017-1137-y
          10.1007/s00360-017-1137-y
          29189935
          fdce96c6-bd47-4a32-8c1d-88e60c0e8abc
          History

          Acid–base regulation,Alkalinity,Ammonia,Ionoregulation,Nitrogen quotient,Oxygen consumption,Urea

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