Journal of comparative physiology

, Volume 144, Issue 2, pp 261–270 | Cite as

Plasma homeostasis and cloacal urine composition inCrocodylus porosus caught along a salinity gradient

  • Gordon C. Grigg
Article

Summary

Juveniles of the Estuarine or Saltwater Crocodile,Crocodylus porosus, maintain both osmotic pressure and plasma electrolyte homeostasis along a salinity gradient from fresh water to the sea. In fresh water (FW) the cloacal urine is a clear solution rich in ammonium and bicarbonate and containing small amounts of white precipitated solids with high concentrations of calcium and magnesium. In salt water (SW) the cloacal urine has a much higher proportion of solids, cream rather than white in colour, which are the major route for excretion of potassium in addition to calcium and magnesium. Neither liquid nor solid fractions of the cloacal urine represent a major route for excretion of sodium chloride. The solids are urates and uric acid, and their production probably constitutes an important strategy for water conservation byC. porosus in SW. These data, coupled with natural history observations and the recent identification of lingual salt glands, contribute to the conclusion thatC. porosus is able to live and breed in either fresh or salt water and may be as euryhaline as any reptile.

Keywords

Magnesium Bicarbonate Uric Acid Sodium Chloride Osmotic Pressure 

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Copyright information

© Springer-Verlag 1981

Authors and Affiliations

  • Gordon C. Grigg
    • 1
  1. 1.Zoology, A08University of SydneySydneyAustralia

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