The alkaline tide goes out and the nitrogen stays in after feeding in the dogfish shark, Squalus acanthias

Chris M. Wood, Carol Bucking, John Fitzpatrick, Sunita Nadella

Research output: Contribution to journalArticlepeer-review

47 Scopus citations


In light of previous work showing a marked metabolic alkalosis ("alkaline tide") in the bloodstream after feeding in the dogfish shark (Squalus acanthias), we evaluated whether there was a corresponding net base excretion to the water at this time. In the 48 h after a natural voluntary meal (teleost tissue, averaging 5.5% of body weight), dogfish excreted 10,470 μmol kg-1 more base (i.e. HCO3- equivalents) than the fasted control animals (which exhibited a negative base excretion of -2160 μmol kg-1). This large activation of branchial base excretion after feeding thereby prevented a potentially fatal alkalinization of the body fluids by the alkaline tide. The rate peaked at 330 μmol kg-1 h-1 at 12.5-24 h after the meal. Despite a prolonged 1.7-fold elevation in MO2 after feeding ("specific dynamic action"), urea-N excretion decreased by 39% in the same 48 h period relative to fasted controls. In contrast, ammonia-N excretion did not change appreciably. The N/O2 ratio declined from 0.51 in fasted animals to 0.19 in fed sharks, indicating a stimulation of N-anabolic processes at this time. These results, which differ greatly from those in teleost fish, are interpreted in terms of the fundamentally different ureotelic osmoregulatory strategy of elasmobranchs, and recent discoveries on base excretion and urea-retention mechanisms in elasmobranch gills.

Original languageEnglish (US)
Pages (from-to)163-170
Number of pages8
JournalRespiratory Physiology and Neurobiology
Issue number2
StatePublished - Nov 15 2007


  • Ammonia
  • Base excretion
  • Feeding
  • Specific dynamic action
  • Urea

ASJC Scopus subject areas

  • Physiology
  • Pulmonary and Respiratory Medicine
  • Neuroscience(all)


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