Urea based osmoregulation and endocrine control in elasmobranch fish with special reference to euryhalinity

• Published in: Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology
• Main Authors: Hazon, N., Wells, A., Pillans, R. D., Good, J.n P., Anderson, W. G., Franklin, C. E.
• Other Authors: Mommsen, Thomas P. (Editor-in-Chief), Walsh , Patrick J. (Editor-in-Chief)
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier Science 2003
• Subjects: Zoology; Euryhaline; Elasmobranch; Osmoregulation; Gill; Kidney; Rectal Gland; Drinking; Urea; Na+; Cl-; Dogfish Squalus-acanthias; Lesser-spotted Dogfish; Rectal Gland-function; Renin-angiotensin System; Stingray Dasyatis-sabina; Cell-volume Regulation; Body-fluid Regulation; Skate Raja-erinacea; Scyliorhinus-canicula; Spiny Dogfish; 270604 Comparative Physiology; C1; 780105 Biological sciences; 0601 Biochemistry and Cell Biology; Canicula; spiny dogfish; Squalus acanthias
• Online Access: https://espace.library.uq.edu.au/view/UQ:66628

Since the landmark contributions of Homer Smith and co-workers in the 1930s there has been a considerable advance in our knowledge regarding the osmoregulatory strategy of elasmobranch fish. Smith recognised that urea was retained in the body fluids as part of the 'osmoregulatory ballast' of elasmobranch fish so that body fluid osmolality is raised to a level that is iso- or slightly hyper-osmotic to that of the surrounding medium. From studies at that time he also postulated that many marine dwelling elasmobranchs were not capable of adaptation to dilute environments. However, more recent investigations have demonstrated that, at least in some species, this may not be the case. Gradual acclimation of marine dwelling elasmobranchs to varying environmental salinities under laboratory conditions has demonstrated that these fish do have the capacity to acclimate to changes in salinity through independent regulation of Na+, Cl- and urea levels. This suggests that many of the presumed stenohaline marine elasmobranchs could in fact be described as partially euryhaline. The contributions of Thomas Thorson in the 1970s demonstrated the osmoregulatory strategy of a fully euryhaline elasmobranch, the bull shark, Carcharhinus leucas, and more recent investigations have examined the mechanisms behind this strategy in the euryhaline elasmobranch, Dasyatis sabina. Both partially euryhaline and fully euryhaline species utilise the same physiological processes to control urea, Na+ and Cl- levels within the body fluids. The role of the gills, kidney, liver, rectal gland and drinking process is discussed in relation to the endocrine control of urea, Na+ and Cl- levels as elasmobranchs acclimate to different environmental salinities. (C) 2003 Elsevier Inc. All rights reserved.