The influence of diet composition and tissue type on the stable isotope incorporation patterns of a small‐bodied southern African minnow Enteromius anoplus (Cypriniformes, Cyprinidae)

Abstract

Rationale In trophic ecology, the use of stable isotope data relies on the general understanding of isotope turnover rates and diet‐to‐tissue discrimination factors (DTDFs). Recent studies on the application of stable isotope data have shown that isotope turnover rates and DTDFs can be influenced by many factors, including diet composition and tissue type. This study investigated the influence of diet composition and tissue type on stable isotope incorporation patterns in a small‐bodied African minnow, the chubbyhead barb Enteromius anoplus. Methods The isotopic incorporation patterns of carbon (δ13C values) and nitrogen (δ15N values) into white muscle and caudal fin tissues of the chubbyhead barb were examined using two isotopically different diets. Controlled‐diet stable isotope feeding trials using a fishmeal‐based diet (diet 1) and a soya‐based diet (diet 2) were conducted over a 180‐day period for the chubbyhead barb. Results The two diets had contrasting isotopic incorporation patterns: diet 1 was associated with progressively high δ13C and δ15N values, whereas diet 2 was associated with progressively low δ13C and δ15N values over time for both muscle and fin tissues. The δ13C turnover rates were similar for both tissues (56 and 61 days), whereas the δ15N turnover rates differed between fin and muscle tissue in both diets (diet 1 = 4 and 130 days, and diet 2 = 72 and 300 days, respectively). The DTDFs were similar for both tissues in diet 1 (Δ13C: −3.96 to −2.62‰, Δ15N: 1.98 to 2.61‰) and diet 2 (Δ13C: 4.05 to 5.24‰, Δ15N: 8.45 to 9.69‰). Conclusions These results suggest that fin tissue can potentially be used as an alternative for muscle tissue in food web studies with a reasonable level of error. The isotopic turnover rate and DTDFs estimates for E. anoplus, however, require consideration of diet composition because different diets may differ in their isotopic incorporation patterns.

Exploring source differences on diet-tissue discrimination factors in the analysis of stable isotope mixing models

“…Thus, the general fast turnover in muscle compared to fin tissue suggests either differences in protein and lipid content 72 or high muscle turnover compared to fin tissue. Although this observation appeared to be consistent with some studies 38 , 42 , other studies have, nonetheless, reported faster turnover and low isotope enrichment in fin tissues compared to muscle tissue 37 , 63 , 71 . These variations therefore highlight the importance of interspecific differences in isotope incorporation and the need to understand the aspects related to tissue metabolism.…”

“…For example, DeNiro and Epstein 17 showed that trophic enrichment of varied in relation to source values because the metabolic biochemical fractions would directly depend on both the quantity and quality of dietary isotope values. Recent empirical studies on fishes have also shown that different diet sources can yield considerable variation in both tissue turnover rates and 36 , 42 , 62 , 63 . Similarly, an extensive review by Caut et al 29 on several animal taxa reported wide ranging values (− 8.8 to 6.1‰) due to several factors, including diet kinetic effects during catabolism and macromolecule synthesis.…”

“…Although empirical studies on DTDFs and isotope turnover rates have been crucial in understanding the dynamics of isotope incorporation in animal tissues 24 , 39 , the use of this information in isotope mixing models remains limited 40 – 42 , in part, because such information is either unavailable for a wide range of taxa or its acquisition may be costly and impractical. Consequently, many studies on mixing models rely on proxy DTDFs that are derived either from previous studies (e.g.…”

“… 46 , 47 ), highlights the need to explore the use of experimentally-derived DTDFs that are informative. Recent studies on freshwater fishes based on both laboratory 36 , 42 and field 40 , 41 research have already shown that variations in DTDFs for both and isotopes have implications for interpreting food webs. The present study, therefore, explores the utility of isotope mixing models, and how their interpretation can be influenced by the use of either literature-based or empirically-derived diet-tissue discrimination factors.…”

“…First, following the recent observations in empirical studies on stable isotope feeding trials on different fish taxa (e.g. 36 , 38 , 42 , 49 ), our study explored the variation in both diet sources with different stable isotope values and different body tissues in relation to stable isotope incorporation and diet-to-tissue discrimination patterns. Specifically, the present study hypothesized that isotope incorporation rates and DTDFs would vary both for diet sources with different and values and for different body tissues of the study species.…”