Direct effects of ambient ammonia on the nitrogen isotope ratios of fish tissues

Onour Moeri, Leonel Da Silveira Lobo Sternberg, Lenore Polo Rodicio, Patrick J. Walsh

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


We tested the assumption that the nitrogen isotope ratios of fish are solely determined by their diet by exposing two species offish having contrasting nitrogen metabolic profiles to 15N ammonia. Beaugregory damselfish (Stegastes leucostictus) representing ammonotelic species and toadfish (Opsanus beta) representing ureotelic species were exposed to 15N ammonia for a period of 4 weeks, after which muscle and liver tissues were analyzed for 15N abundance and compared to their respective control group. Both species showed significant 15N enrichment when exposed to 15N ammonia, with the ammonotelic fish showing a greater enrichment compared to the ureotelic fish. We propose that the toadfish showed less enrichment in its muscle tissue because its active omithine-urea cycle (O-UC) rapidly sequesters ammonia away from the circulatory system and into liver tissue, thereby preventing any substantial exchange between ammonia and muscle tissue. We propose that no such sequestering occurs in the ammonotelic damselfish because they lack a functional O-UC. These results have important implications for studies using nitrogen isotope ratios to delineate trophic structure in aquatic ecosystems.

Original languageEnglish (US)
Pages (from-to)61-66
Number of pages6
JournalJournal of Experimental Marine Biology and Ecology
Issue number1-2
StatePublished - Jan 8 2003
Externally publishedYes


  • Ammonia
  • Ammonotele
  • Damselfish
  • Nitrogen isotope ratios
  • Toadfish
  • Trophic level
  • Ureotele

ASJC Scopus subject areas

  • Aquatic Science
  • Ecology, Evolution, Behavior and Systematics
  • Ecology


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