, Volume 91, Issue 2, pp 90–93 | Cite as

Individual protein balance strongly influences δ15N and δ13C values in Nile tilapia, Oreochromis niloticus

  • Julia Gaye-Siessegger
  • Ulfert Focken
  • Hansjörg Abel
  • Klaus Becker
Short Communication


Although stable isotope ratios in animals have often been used as indicators of the trophic level and for the back-calculation of diets, few experiments have been done under standardized laboratory conditions to investigate factors influencing δ15N and δ13C values. An experiment using Nile tilapia [Oreochromis niloticus (L.)] was therefore carried out to test the effect of different dietary protein contents (35.4, 42.3, and 50.9%) on δ15N and δ13C values of the whole tilapia. The fish were fed the isoenergetic and isolipidic semi-synthetic diets at a relatively low level. δ15N and δ13C values of the lipid-free body did not differ between the fish fed the diets with different protein contents, but the trophic shift for N and C isotopes decreased with increasing protein accretion in the individual fish, for N from 6.5‰ to 4‰ and for C in the lipid-free body from 4‰ to 2.5‰. This is the first study showing the strong influence of the individual protein balance to the degree to which the isotopic signature of dietary protein was modified in tissue protein of fish. The extrapolation of the trophic level or the reconstruction of the diet of an animal from stable isotope ratios without knowledge of the individual physiological condition and the feeding rate may lead to erroneous results.


Nile Tilapia Stable Isotope Ratio Dietary Crude Protein Dietary Protein Content Scenedesmus Acutus 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



This study was partly funded by a DFG grant to Dr. U. Focken (FO 267/8-1). The authors wish to thank R. Langel, Georg-August University of Göttingen, for analysis of the isotopic ratios, Dr. H. Richter for critical reading of the manuscript, and B. Fischer for support in the laboratory.


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Copyright information

© Springer-Verlag 2004

Authors and Affiliations

  • Julia Gaye-Siessegger
    • 1
  • Ulfert Focken
    • 1
  • Hansjörg Abel
    • 2
  • Klaus Becker
    • 1
  1. 1.Department of Aquaculture Systems and Animal Nutrition in the Tropics and SubtropicsUniversity of Hohenheim (480b)StuttgartGermany
  2. 2.Institute for Animal Physiology and Animal NutritionGeorg August University GöttingenGöttingenGermany

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