## 1 Introduction  
Food authenticity is of particular interest for both consumers and producers. Consumers are interested in local products of good quality. Therefore, the geographical origin and authenticity of foodstuff are of increasing interest [1]. However, the growing demand for food has led to fraud and adulteration, which are quite often phenomena in food markets. More specifically, adulteration of food with cheaper and lower quality components can lead to food fraud that could affect consumers and producers and face financial impacts and public health risks [2, 3]. Over the last decades, a rapid evolution in fish production has been observed. Aquatic foods are a substantial part of the food commerce. They are composed of omega-3 fatty acids, vitamins, minerals, trace elements, high-quality protein, and essential amino acids; thereby, they improve nutrition, health, and well-being [4]. Fish consumption and demand have increased due to the health advantages and have led to the development of the aquaculture industry [5]. Therefore, the continuous rise lurks a lot of risks to security and safety in seafood consumption, such as food fraud, diseases, and food contamination that can occur along the food chain [6; 7; 8; 9]. In addition, the need for determining food authenticity led the European Union to institute a Traceability Regulation (178/2002/EC). It came into force in January 2005 and defines \"food and feed traceability.\" Moreover, for foods with Protected Geographical Indications (PGI), Protected Designations of Origin (PDO), and Traditional Specialties Guarantee (TSG), European laws EC N. 510/2006 and 1151/2012 require protection against mislabeling [8]. The mullet (_Mugil Cephalus_) is a fish species that can be found in littoral waters. Roes, which are the mullet's eggs, are taken out from the fish and, after a treatment of salting and drying, produces seafood that is named alternatively according to the area that is produced, like Greek \"Avgotaracho\" (see Figure 1), Japanese Karasumi, or Italian Bottarga [10]. A very important tool in food safety strategy is traceability systems. Several analytical methods have been proposed to discriminate the geographical origin of food products. Modern instruments and techniques have been used for the accurate identification of the geographical origin of products; such techniques include plasma laser induced breakdown spectroscopy (LIBS); fourier-transform infrared spectroscopy (FTIR); near-infrared (NIR) and mid-infrared (MIR) spectroscopy; chromatographic techniques, such as gas chromatography-mass spectrometry (GC-MS) or high-performance liquid chromatography (HPLC); nuclear magnetic resonance (NMR); electron spin resonance (ESR); polymerase chain reaction (PCR); enzymatic assays (ELISA); DNA based techniques; and isotope-ratio mass spectrometry (IRMS) with high measurement accuracy, which were developed to serve this need [11]. Amongst them, stable isotope ratio analysis has proven to respond well to adulteration detection of agri-food products. Stable isotope analysis gives information about the geographical origin of various food products, such as juice, wine, milk, honey, oil, and meat [11; 12; 13; 14; 15; 16]. Few studies have been conducted on isotopic analysis for the determination of seafood, and most of them deal with the discrepancy between farmed and non-farmed products [17; 18; 19; 20; 21; 22; 23; 24; 25]. [PERSON] et al. (2015) were the first who investigated the geographical origin of commercial fish by using stable isotope ratio analysis [12]. In particular, they used stable isotope analysis for the discrimination of shrimp and hairtail fish and found that \(\delta^{13}\)C and \(\delta^{15}\)N ratios can be used to differentiate the geographic origin of the samples of the same kind. [PERSON] et al. (2003) referred to the possibility that stable isotope ratio analysis can be applied for the determination of fish seafood products' geographical origin [26]. [PERSON], et.al.