Feeding level and individual metabolic rate affect ?13C and ?15N values in carp: implications for food web studies

Abstract

Stable isotope analyses are often used to calculate relative contributions of multiple food sources in an animal's diet. One prerequisite for a precise calculation is the determination of the diet-tissue fractionation factor. Isotopic ratios in animals are not only affected by the composition of the diet, but also by the amount of food consumed. Previous findings regarding the latter point are controversial. As stable isotope analyses have often been used to investigate aquatic food webs, an experiment with carp (Cyprinus carpioL.) was carried out to test the influence of the feeding level and individual metabolic rate on delta(13)C and delta(15)N values of the whole body. After an initial phase, 49 carp were assigned randomly to four groups and fed the same diet at different levels for 8 weeks. For 15 fish, the energy budget was determined by indirect calorimetry. Feed and individual fish were analysed for their proximate composition, gross energy content and delta(13)C and delta(15)N values. delta(13)C and delta(15)N values differed significantly at different feeding levels. While delta(13)C values of the lipids and delta(15)N values decreased with increasing feeding rate, delta(13)C values of the lipid-free matter showed a non-linear pattern. Data obtained from fish held in the respirometric system revealed a relationship between delta(13)C values and the percentage retention of metabolizable energy. Our results show that reconstructing the diets of fish from the isotopic ratios when the feeding level and individual metabolic rates are unknown would introduce an error into the data used for back-calculation of up to 1 per thousand for both delta(13)C and delta(15)N values and may have substantial effects on the results of calculated diets. As other workers have pointed out, the development and application of stable isotopes to nutritional ecology studies is a field in its infancy and gives rise to erroneous, misleading results without nutritional, physiological and ecological knowledge.

Stable carbon and nitrogen incorporation in blood and fin tissue of the catfish Pterygoplichthys disjunctivus (Siluriformes, Loricariidae)

“…It has been hypothesized that food-deprived animals catabolize their own tissues for energy and maintenance, and hence, become more enriched in 15 N over time (McCue and Pollock 2008;Martínez del Rio et al 2009). In support of this, carp fed a ration sufficient only for body mass maintenance for 56 days showed a 0.5‰ increase in whole body δ 15 N in comparison to starting values (Gaye-Siessegger et al 2004). Additionally, salmon at the end of migration (~133 days without feeding) had liver δ 15 N values that were 1.5‰ enriched in comparison to the beginning of migration (Doucett et al 1999).…”

Trophic typology of coastal ecosystems based on δ13C and δ15N ratios in an opportunistic suspension feeder

“…Nevertheless, isotopic fractionation values may be influenced by species and biochemical forms of excretion (Vanderklift & Ponsard 2003, Dubois et al 2007a), age (Overman & Parrish 2001, tissue biochemical composition (Lorrain et al 2002), diet and food quality (Hobson & Clark 1992, McCutchan et al 2003, feeding level and nutritional status (Hobson et al 1993, Gaye-Siessegger et al 2004, environmental abiotic parameters (Vanderklift & Ponsard 2003, Sweeting et al 2007, and even by methods of sample preparation (McCutchan et al 2003). Some of these sources of variability, specifically, species, age, and methods of sample preparation, could not have caused differences in oyster muscle isotopic values among our 8 systems.…”

“…Gaye-Siessegger et al 2004, Barnes et al 2007). Indeed, starvation and low feeding levels of the Nile tilapia Oreochromis niloticus resulted in enrichment of 13 C in lipids and 15 N in protein (Gaye-Siessegger et al 2007).…”

Relationship between efficiency of nitrogen utilization and isotopic nitrogen fractionation in dairy cows: contribution of digestion v. metabolism?

“…It has been shown across a variety of conditions that 15 N natural abundance (δ 15 N; 15 N/ 14 N ratio relative to atmospheric N 2 ) in animal proteins is higher than in the diet consumed (DeNiro and Epstein, 1981) and that variations in this isotopic N fractionation (Δ 15 N animal-diet = δ 15 N animal − δ 15 N diet ) are closely and negatively correlated with ENU in different species (Gaye-Siessegger et al, 2004;Cheng et al, 2013;Cantalapiedra-Hijar et al, 2015). The more efficiently the animals assimilate dietary N, the closer are the δ 15 N values in animal proteins and diet (i.e.…”

“…The more efficiently the animals assimilate dietary N, the closer are the δ 15 N values in animal proteins and diet (i.e. lower Δ 15 N animal-diet ), and this may apply at the individual animal level (Gaye-Siessegger et al, 2004;Poupin et al, 2014;Wheadon et al, 2014). Therefore, Δ 15 N animal-diet could be used to classify individuals receiving the same diet by their ENU.…”