Turnover and fractionation of nitrogen stable isotope in tissues of grass carp Ctenopharyngodon idellus

Abstract

Determination of the isotopic turnover rate in the various tissues of an organism is one of the essential prerequisites for tracing the food sources of consumers and for elucidating trophic interactions in ecological studies using stable isotope analysis (SIA). Isotopic turnover and fractionation in the commercially important freshwater teleost grass carp Ctenopharyngodon idellus, however, are poorly understood so far. In the present study, we conducted a diet-switch experiment of C. idellus for 3 mo to assess nitrogen isotopic turnover and fractionation in different tissues of this species, including liver, muscle, and gill. The results revealed that turnover rates exhibited significant differences between tissues and increased in the sequence of gill < muscle < liver, owing to the differences in metabolic activities between the tissues. Contribution to longterm nitrogen isotopic turnover rates from metabolism was greatest for the liver (~70 to 77% metabolic contribution) and greatest from growth for the gill (86 to 90% contribution of net tissue increase). Nitrogen half-lives estimated with time-or growth-based models were, respectively, 29.9 d and 1.18-fold mass increase for liver, 68.3 d and 1.45-fold mass increase for muscle, and 115.4 d and 1.81-fold mass increase for gill. The nitrogen isotopic fractionation of all tissues was enriched by 3 to 4 ‰ relative to the nitrogen isotopic signature of the diet, with significant differences between the 3 types of tissues, probably owing to the different biochemical pathways and constituents between the various tissues. : 177-186, 2013 fractionation between trophic levels relative to carbon and sulfur (Post 2002). KEY WORDS: Ctenopharyngodon idellus · Nitrogen isotopic turnover · Metabolism · Growth · Fractionation Resale or republication not permitted without written consent of the publisher OPEN PEN ACCESS CCESSAquacult Environ Interact 3After a consumer is provided with an isotopically distinct diet, the isotopic ratios of its tissues will change as a consequence of 2 general processes: catabolic breakdown and anabolic replacement. The isotopic turnover rate depends on both the growth rate, representing the synthesis from the new diet in excess of breakdown; and the metabolic rate, representing the balanced rate of breakdown of old tissue synthesized during feeding on a previous diet and resynthesis of tissue components made from the new diet (Hesslein et al. 1993, MacAvoy et al. 2005. With known growth rates, the proportional contributions of metabolism and growth to stable isotopic turnover can be estimated from nonlinear regressions of the isotopic turnover trajectories based on both time and growth models (Buchheister & Latour 2010). Previous studies have showed that the contribution of metabolic replacement to the total isotopic turnover rate is negligible or of minor importance for the juveniles of ectothermic species, and growth is the primary factor driving the turnover of stable isotopes due to the low metabolic activities of ectothermic an...

Tissue-specific turnover rates of the nitrogen stable isotope as functions of time and growth in a cyprinid fish

“…Other studies have, however, revealed that considerable differences in turnover rates can be apparent between fish tissues (Buchheister & Latour, 2010;Xia et al, 2013b), although their differences are often only minor (Hesslein et al, 1993;Sweeting et al, 2005;McIntyre & Flecker, 2006). Thus, tissue turnover differentiation, as well as the relative ordering of turnover rates among tissues, appears to be speciesspecific.…”

“…Buchheister and Latour (2010) studied summer flounder Paralichthys dentatus (Linnaeus, 1766) liver, blood and muscle tissue and found muscle had the slowest half-life (85 days). For grass carp Ctenopharyngodon idellus (Valenciennes, 1844), the estimated 15 N half-life of muscle was 68 days (Xia et al, 2013b). Where differences between tissue turnover rates are detected in fishes, they generally follow the pattern that more metabolically active tissues show faster stable isotope turnover rates (Tieszen et al, 1983).…”

“…In the experiment, the stable isotope data reflected and approached those of their new diet at the end of second feeding period, although predictions were that isotopic equilibrium had not been reached. Predicting the turnover processes using a range of turnover models (Buchheister & Latour, 2010;Xia et al, 2013b) revealed that in the best-fitting models, muscle had the shortest turnover time, followed by fin and then scales.…”

Carbon stable isotope turnover and fractionation in grass carp Ctenopharyngodon idella tissues

“…Resale or republication not permitted without written consent of the publisher carried out, especially for unstudied species (Fisk et al 2009, Xia et al 2013b.…”

Carbon, nitrogen and phosphorus budgets of silver carp Hypophthalmichthys molitrix with the co‑culture of grass carp Ctenopharyngodon idella

“…Its production has increased rapidly over recent decades (Xia et al 2013a(Xia et al , 2013b. However, the high stocking density with an artificial supply of formulated feed has resulted in a large amount of effluents.…”