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Journal of Comparative Physiology B

, Volume 163, Issue 1, pp 70–77 | Cite as

Osmoregulation of the Australian freshwater crocodile, Crocodylus johnstoni, in fresh and saline waters

  • L. E. Taplin
  • G. C. Grigg
  • L. Beard
Article

Abstract

An unusual saltwater population of the “freshwater” crocodilian, Crocodylus johnstoni, was studied in the estuary of the Limmen Bight River in Australia's Northern Territory and compared with populations in permanently freshwater habitats. Crocodiles in the river were found across a large salinity gradient, from fresh water to a salinity of 24 mg · ml-1, more than twice the body fluid concentration. Plasma osmolarity, concentrations of plasma Na+, Cl-, and K+, and exchangeable Na+ pools were all remarkably constant across the salinity spectrum and were not substantially higher or more variable than those in crocodiles from permanently freshwater habitats. Body fluid volume did not vary; condition factor and hydration status of crocodiles were not correlated with salinity and were not different from those of crocodiles from permanently fresh water. C. johnstoni clearly has considerable powers of osmoregulation in waters of low to medium salinity. Whether this osmoregulatory competence extends to continuously hyperosmotic environments is not known, but distributional data suggest that C. johnstoni in hyperosmotic conditions may require periodic access to hypoosmotic water. The study demonstrates a physiological capacity for colonisation of at least some estuarine waters by this normally stenohaline freshwater crocodilian.

Key words

Osmoregulation Salt glands Salinity Homeostasis Crocodile, Crocodylus johnstoni 

Abbreviations

ANOCOVA

analysis of covariance

BW

body weight

CF

condition factor

ExNa

exchangeable sodium

HF

hydration factor

SVL

snout-vent length

TBW

total body water

THO

tritiated water

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Copyright information

© Springer-Verlag 1993

Authors and Affiliations

  • L. E. Taplin
    • 1
  • G. C. Grigg
    • 1
  • L. Beard
    • 1
  1. 1.School of Biological SciencesThe University of SydneyAustralia

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