Nitrogen metabolism and excretion in an intertidal population of the gulf toadfish (Opsanus beta)

T. E. Hopkins, C. M. Wood, P. J. Walsh

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


The present study was undertaken to assess the ability of gulf toadfish (Opsanus beta) from an intertidal population in northern Florida to make and excrete urea as a nitrogenous waste product. Using an electronic tide gauge and data logger, we were able to demonstrate that toadfish in the intertidal mudflats at Panacea. Florida were air-exposed approximately 9.3% of the over 2000 h monitored, and that these periods could last as long as 9 h. Toadfish were collected from this site during several seasons in 1993-1994, and were subjected to experiments which measured their nitrogenous waste production (as ammonia and urea). Samples were also analyzed for several biochemical proxies of urea excretion (including liver ornithine-urea cycle (O-UC) enzyme activities, and activities of nitrogen feeder enzymes, including the key enzyme glutamine synthetase. G Sase), as well as plasma cortisol, urea and other variables. Although freshly collected toadfish from Panacea exhibited relatively high activities of the O-UC enzymes, they showed rather low activities of GSase, indicating a low potential for immediate urea production. Furthermore, urea excretion rates were extremely low during the first 24-36 h in captivity, even when toadfish were subjected to an experimental emersion period of 8 h intended to simulate air-exposure in nature. When compared to responses and values of subtidal toadfish from Biscayne Bay. Florida published in a prior report, and from a single sample of subtidal toadfish at Panacea, it is apparent that urea synthesis and excretion in the gult toadfish are likely not a direct consequence of air-exposure during the tidal cycle. Our data are discussed in the context of an ammonia-exposure hypothesis explaining urea synthesis and excretion in this species.

Original languageEnglish (US)
Pages (from-to)21-34
Number of pages14
JournalMarine and Freshwater Behaviour and Physiology
Issue number1
StatePublished - 1999
Externally publishedYes


  • Ammonia
  • Gulf toadfish
  • Intertidal
  • Opsamus beta
  • Urea
  • Ureogenesis

ASJC Scopus subject areas

  • Aquatic Science
  • Oceanography


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