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|  Fish also has a non-protein nitrogen (NPN) fraction made of water-soluble, low molecular weight, nitrogen-containing compounds of a non-protein nature. This NPN-fraction constitutes from 9 to 18 percent of the total nitrogen in teleosts, including trimethylamine oxide (TMAO), free amino acids, creatine andcarnosine. Despite their low levels, the constituents of the NPN fraction play a major role in fish quality.Nutritional elements of fish Fish is highly nutritious, tasty and easily digested. It is much sought after by a broad cross-section of the world's population, particularly in developing countries. It is estimated that around 60 percent of people in many developing countries depend on fish for over 30 percent of their animal protein supplies, while almost 80 percent in most developed countries obtain less than 20 percent of their animal protein from fish. However, with the increased awareness of the health benefits of eating fish and the ensuing rise in fish prices, these figures are rapidly changing. | | | | Fish products are comparable to meat and dairy products in nutritional quality, depending on the methods used in preservation and preparation. The protein content of most fish averages 15 to 20 percent. Fish also contains significant amounts of all essential amino acids, particularly lysine in which cereals are relatively poor. Fish protein can be used therefore to complement the amino acid pattern and improve the overall protein quality of a mixed diet. Moreover, the sensory properties of an otherwise bland diet can be enhanced through fish products, thus facilitating and contributing to greater consumption. | | | | Whereas cereal grains are usually low in lysine and/or the sulphur-containing amino acids (methionine and cysteine), fish is an excellent source of these acids. A fish supplement can significantly raise the biological value of a cereal-based diet. | | | | Also, fish meat is generally a good source of the B vitamins and, in the case of fatty species, of A and D vitamins. Some freshwater species such as carp have high thiaminase activity so the thiamine content in these species is usually low. As for minerals, fish meat is a particularly valuable source of calcium and phosphorus as well as iron, copper and selenium. Saltwater fish have a high content of iodine. | | | | In addition to essential amino acids and proteins, fish nutritional attributes relate to the quality of lipids and vitamin and mineral content. | | | | In human nutrition, fatty acids such as linoleic and linolenic acid - important for preventing skin diseases - are considered essential as they cannot be synthesised by the organism. In marine fish, these fatty acids constitute only around two percent of the total lipids - a small percentage compared with many vegetable oils. However, fish oils contain other "essential" polyunsaturated fatty acids which act in the same way as linoleic and arachidonic acids. As members of the linolenic acid family (first double bond in the third position, w-3 counted from the terminal methyl group), they also have neurological benefits in growing children. One of these fatty acids, eicosapentaenoic (C20: 5 w 3), has attracted considerable attention since Danish scientists found a significant presence of it in the diet of a group of Greenland Eskimos who proved virtually free from arteriosclerosis. Studies in the United Kingdom and elsewhere have documented that eicosapentaenoic acid in the blood is an extremely potent anti-thrombotic factor. | | | | |
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