Field studies on the ureogenic gulf toadfish, in a subtropical bay. II. Nitrogen excretion physiology

T. E. Hopkins, J. E. Serafy, P. J. Walsh

Research output: Contribution to journalArticlepeer-review

27 Scopus citations


In order to examine the in situ nitrogen excretion physiology of gulf toadfish (Opsamus beta) (Fam. Batrachoididae), several biochemical and physiological measurements relating to urea synthesis and excretion were measured in samples taken from freshly collected gulf toadfish from a subtidal population in Biscayne Bay, Florida, U..A. This indirect approach was used, instead of direct measurements of nitrogen excretion, because nitrogen excretion patterns of gulf toadfish are altered markedly during the first 24 h of capture disturbance or laboratory confinement. The values obtained for plasma cortisol levels, and the activities of hepatic ornithine urea cycle enzymes, including glutamine synthetase (and its partitioning between cytosolic and mitochondrial compartments), suggest that gulf toadfish in Biscayne Bay may excrete a substantial portion of their waste nitrogen as urea. Also conducted were correlation analyses of several biotic variables (plasma [cortisol], enzyme activities, plasma [urea], hepatosomatic index, and plasma[Ca++]) wit several abiotic variables (temperature, sanity, depth and dissolved oxygen), and with collection site and season. Results of these analyses are discussed in the context of hypotheses to explain ureotely in this teleost fish.

Original languageEnglish (US)
Pages (from-to)1271-1284
Number of pages14
JournalJournal of Fish Biology
Issue number6
StatePublished - Jun 1997
Externally publishedYes


  • Cortisol
  • Glutamine synthetase
  • Ornithine-urea cycle enzymes
  • Urea
  • Ureotely

ASJC Scopus subject areas

  • Aquatic Science


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