## 4 Metabolomics for Metabolite Detection in Aquatic Food Products
### Chemical Contaminants  
Aquatic food products are one of the most important cardioprotective food groups with beneficial effects on human health because of the unsaturated fatty acids and primarily polyunsaturated fatty acids, which are found in abundance [1]. Nevertheless, there are also potential hazards since it may contain specific industrial or environmental contaminants, such as pathogens, dye residues, marine toxins, and environmental pollutants (including heavy metals). For example, methylmercury or persistent organic pollutants (POPs) like DDT, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and organochlorine pesticides (OCPs) can have hazardous effects on human health like immune toxicity, reproductive toxicity, neurotoxicity, gene mutations, and DNA methylation after long-term exposure at low levels. They are also known to have negative economic impacts [75; 97; 110]. Measuring and documenting these effects can function as an indicator of environmental conditions and as an aquatic animal health surveillance, consequently helping to protect an important source of human food [124]. According to the Food and Agriculture Organization (FAO), maximum levels of environmental chemical contaminants have been established for a number of compounds (Table 3). In order to guarantee a high level of protection for human health, a thorough legal framework was developed. The European Parliament and the Council of the European Union have adopted Regulation (EU) No. 1379/2013 [126], according to which fishery and aquaculture products should comply with applicable rules on food safety and hygiene and provide clear and comprehensive information on the origin and the method of production. Moreover, both the commercial and scientific name are required. Additionally, national authorities should make full use of available technology, including DNA testing, in order to deter operators from falsely labeling catches in order to protect consumers. Undoubtedly, omic technologies could be a complimentary analytical tool to existing analytical DNA-based methods. Proteomic technologies, for example, can provide comprehensive information of the whole system enclosing co-transcriptional modifications, giving the ability of a clear and deep understanding of proteins' composition at a molecular level [127]. According to [PERSON] et al. [97], studies have shown that environmental pollutants and toxic metals cause changes in the proteome of seafood, indicating a detrimental impact on aquatic food product quality. More specifically, the alteration of physio-metabolic response and the activation of proteins and metabolites are associated with the detoxication and degradation of structural proteins degradation, such as actin, myosin, and desmin. Metabolites could also be reliable markers of the physiological and biochemical status in organisms. Thus, the metabolic abnormalities could be used to elucidate and understand the physiological responses and biochemical reactions provoked by exogenous factors like pollutants [77]. Metabolomic technologies like mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy could be used in order to detect these minor metabolic abnormalities in stress-exposed tissue samples and, as a result, to interpret the aforementioned physiological responses and biochemical reactions [77; 79; 80; 128]. In the framework of the [PERSON] et al. [77] study, NMR metabolomic technology was used for detecting metabolic changes and determining the metal pollution-induced biological effects in the muscle tissues of shrimp (_Fenneropenaeus chinensis_). According to [PERSON] et al. [74], metabolomics analysis in largemouth bass (_Microterus alloides_) based on copper (Cu) exposure revealed that after supplemented with 1%, 3%, and 5% of hydrolysis fish peptides, 85, 144, and 207 differential metabolites were identified in these three different supplemented groups, respectively.