## 1 Introduction  
High workload, stress, and poor diet leads to numerous human diseases in developed European countries. The highest number of deaths in Europe is due to cardiovascular diseases. Slightly over 1.8 million people have died from diseases of the circulatory system, mainly heart attacks and strokes. These are the main causes responsible for 36% of all deaths in the European Union [1]. One of the causes of these unfavourable conditions may be incorrect nutrition with an excess of dietary fats or an excessive intake of saturated fatty acids (SFA). The recommended intakes of total fat and fatty acids for a healthy population (adults, children, and infants) have been published earlier [2]. A number of studies confirm the fact that the quality and quantity of fatty acids in the diet can influence the cardiovascular risk. The benefits of dietary long-chain n-3 polyunsaturated fatty acids (LC n-3 PUFA) on human health were studied and reported through clinical, pathological, observational, and case studies over a long period. Regular intake of polyunsaturated fatty acids (PUFA) in the diet is an important factor for the normal growth, development, and prevention of cardiovascular diseases (CVD) and atherosclerosis in humans [3; 4; 5]. The American Heart Association reported the specific effect of the n-3 polyunsaturated fatty acid (n-3 PUFA) supplementation on clinical cardiovascular events [3]. The LC n-3 PUFA, eicosapentaenoic acid (EPA, 20:5n3), and docosahexaenoic acid (DHA, 22:6n3) are most closely associated with a lower CVD risk [6]. Some authors deal with the preventive effects of PUFA and the nutritional value of fish meat in the diet. Fish meat contains a significantly lower amount of SFA compared to red meat and is beneficial for nutrition due to it being a rich source of LC n-3 PUFA, especially EPA and DHA. Fat is the third major constituent in fish muscle. The fat content varies among species and also among different organs within the species [7; 8; 9; 10]. The fatty acid composition, quality, and fat content of fish meat depends on the fish species, on the age of fish, on the composition of feed, and their origin (wild versus farmed) [11; 12]. Fish oil is also the most important natural source of PUFA, which includes EPA and DHA [13; 14]. In 2002, the American Heart Association (AHA) published a scientific statement on LC n-3 PUFA in marine and freshwater fish and supplements in relation to CVD; they also reported the beneficial effects of LC n-3 PUFA on the prevention of CVD [3]. This recommendation by AHA for using generous quantities of fish in the diet in order to obtain sufficient quantities of protein without excess fatty acids and lipids was supported by other authors [2; 5]. Fish muscle is a good source of n-3 PUFAs that are considered to be the most important in human nutrition due to their therapeutic role in reducing certain cardiovascular disorders [11; 15; 16; 17]. Sufficient intake of n-3 PUFA in the diet prevents arrhythmias, ventricular tachycardia, and fibrillation, inhibits the synthesis of cytokines and mitogens, has anti-inflammatory, antithrombotic, and hypolipidemic properties, with effects on triacylglycerlos (TAG), has very low-density lipoproteins (VLDLs), and can inhibit atherosclerosis [2; 18; 19]. According to older studies, the preventive effect of regular additions of PUFAs in the human diet is obvious. Over the last several decades, a number of authors have reported the beneficial composition of fish meat. Essential polyunsaturated fatty acids such as \(\alpha\)-linolenic acid (18:3 n-3, ALA), EPA and DHA are not synthesized in the human body, but they are synthesized by aquatic organisms. Therefore, humans must receive these essential fatty acids in food. The available resources are marine and freshwater fish [7; 20]. Fish consumption varies from country to country depending on regional use, historical context, access to the sea, and affordability. In landlocked countries, freshwater fish are reared under traditional fish farming conditions [21].