Feeding fish with diets of different ratios of C3- and C4-plant-derived ingredients: a laboratory analysis with implications for the back-calculation of diet from stable isotope data.
Back-calculation of the diet is one of the most frequent applications of stable isotope techniques in animal ecology. These calculations are often based on two assumptions: a constant trophic shift for all dietary items and a linear response of the isotopic ratios to different mixtures of two isotopically distinct feeds. In a laboratory experiment, fish (Nile tilapia, Oreochromis niloticus) were fed semi-synthetic diets prepared either from wheat or corn ingredients, or from three blended diets (25, 50, 75% wheat components). Isotopic analysis of the lipid-free and lipid fraction of the fish after the experiment revealed that the trophic shift was not constant for wheat- and corn-based diets. The isotopic response to the mixed diets was not linear, leading to a statistically significant over-estimation of the corn component in the back-calculation. Both effects are in agreement with published data on the isotopic effects of C3- and C4-plant materials in the diet.
Department of Aquaculture Systems and Animal Nutrition in the Tropics and Subtropics, University of Hohenheim (480B), 70593 Stuttgart, Germany. Focken@uni-hohenheim.de
Ulfert
U
Focken
D000284:Administration, Oral; D000465:Algorithms; D000818:Animals; D002247:Carbon Isotopes / Q000032:analysis* / Q000378:metabolism*; D023681:Cichlids / Q000378:metabolism*; D004032:Diet; D019587:Dietary Supplements / Q000032:analysis*; D004734:Energy Metabolism / Q000502:physiology; D005504:Food Analysis / Q000379:methods*; D005983:Glutens / Q000008:administration & dosage / Q000032:analysis / Q000378:metabolism; D013058:Mass Spectrometry / Q000379:methods; D008954:Models, Biological; D010936:Plant Extracts / Q000008:administration & dosage / Q000032:analysis* / Q000378:metabolism; D010938:Plant Oils / Q000008:administration & dosage / Q000032:analysis / Q000378:metabolism; D013213:Starch / Q000008:administration & dosage / Q000032:analysis / Q000378:metabolism; D014908:Triticum / Q000737:chemistry; D003313:Zea mays / Q000378:metabolism
D002247:Carbon Isotopes; D010936:Plant Extracts; D010938:Plant Oils; D005983:Glutens; D013213:Starch