Application of Nonparametric Multivariate Analyses to the Authentication of Wild and Farmed European Sea Bass (Dicentrarchus labrax). Results of a Survey on Fish Sampled in the Retail Trade

Abstract

The aim of this study was to apply biometric measurements and analyses of proximate composition, fatty acid composition, and ratios of stable isotopes of carbon (δ(13)C) and nitrogen (δ(15)N) in muscle tissue to reliably differentiate between wild and farmed European sea bass (Dicentrarchus labrax). Farmed (n = 20) and wild (n = 19) European sea bass were purchased between March and May 2008 and used as standard samples. In the same months, a survey was conducted to evaluate the truthfulness of the statements on the labels of European sea bass sold in retail markets (declared farmed n = 34 and declared wild n = 33). In addition, data from the literature (reference) were employed to build the profile type of wild and farmed European sea bass. Primarily, an exploration and comparison of the analytical data of the standard data set based on principal component analysis and permutation test were performed. Afterward, an inferential statistical approach based on nonparametric combination test methodology (NPC) was applied on standard samples to check its suitability in discriminating the production method. This multivariate statistical analysis selected 30 variables on a total of 36 available. The validation of standard fish data set was accomplished by a novel nonparametric rank-based method according to profile type (just 1 misclassification over 39 samples). Both the NPC test and nonparametric rank-based method were then applied to survey fishes using the selected variables with the aim to classify the individual European sea bass as "true farmed" or "true wild". The former test segregated 10 fishes over 33 declared wild, whereas the results obtained by the nonparametric rank-based method showed that 11 of 33 declared wild European sea bass samples could be unquestionably attributed to the wild cluster. Moreover, considering the comparative contribution of profile type, a few surveyed farmed samples were ascribed to the wild cluster.

Differentiating the wild or farmed origin of Mediterranean fish: a review of tools for sea bream and sea bass

“…Similar results have been found for sea bass (Table 4); farmed individuals have higher lipid levels than their wild conspecifics, while no clear differences exist for proteins, moisture and ash composition (Alasalvar et al 2002b;Orban et al 2003;Periago et al 2005;Nasopoulou et al 2007;Santaella et al 2007;Fasolato et al 2010;Fuentes et al 2010;Ottavian et al 2012). Therefore, proximal analysis is not a useful technique to determine fish origin, but it provides a basis for further analyses such as metabolic profiling or determining the fatty acid (FA) signature.…”

“…Clear differences exist in the isotopic ratios between wild and farmed fish in different tissues of sea bream (Moreno-Rojas et al 2007;Morrison et al 2007;Serrano et al 2007Serrano et al , 2008 and sea bass (Bell et al 2007;Fasolato et al 2010;Ottavian et al 2012). d13C was consistently lighter in farmed fish than wild fish (Fig.…”

“…The variability in tissue lipid content can alter bulk tissue δ13C values (Focken & Becker ) and could be falsely interpreted as dietary or habitat shifts (Fasolato et al . ).…”

“…; Fasolato et al . ), where wild fish were isotopically enriched in 15N compared with their farmed counterparts. Such differences can be a consequence of the higher trophic level of the fish feed in the natural marine system, but it also may vary according to the manufactured farmed fish diet characteristics reflecting different inputs from terrestrial N sources in farmed sea bass (Fogel & Cifuentes ).…”

“…The condition index is an important tool to measure body shape and acts as a good indicator of dietary condition and history (Grigorakis 2007). Higher condition indices for farmed fish compared with wild fish are observed typically for both sea bream (Flos et al 2002;Rogdakis et al 2011;Arechavala-Lopez et al 2012a) and sea bass (Krajnović-Ozretić et al 1994;Fernandes et al 2007;Fasolato et al 2010;Arechavala-Lopez et al 2012a). The relative profile index and cephalic index have also been suggested as indicators of fish origin for sea bream and sea bass, respectively (Flos et al 2002;Arechavala-Lopez et al 2012a).…”