The lipids

Abstract

From chapter introduction: Students entering the field of fish nutrition might be forgiven for forming two impressions. First, is the impression that because publications on lipids often dominate research journals and conference proceedings on fish nutrition, lipids are the most important nutrients for fish. They are not. Lipids are neither more important nor less important than any of the other groups of nutrients - proteins, carbohydrates, vitamins or inorganic elements. Second, is the impression that because we write more about lipids than other nutrients, we know more about lipids than about other nutrients. We do not. Rather, we probably know less about the nutritional requirements of fish, or any other animal for that matter, for lipids than for other nutrients, which is precisely why there is so much fish lipid nutritional research. Why should this be so? One reason is the relative complexity of lipid chemistry, which is quickly encountered by first time students in the arcane nomenclatures and terminologies of fatty acids. Another, more fundamental reason is that our understanding of the chemistry of the cell’s hydrophobic phase, i.e. of the physico-chemistry of the cell membrane bilayer and the reactions that occur in it, lags well behind our understanding of the cell’s aqueous phase chemistry. In the year 2000 we have a detailed biochemical understanding of amino acids and carbohydrates, their biosynthetic and catabolic pathways, their enzymology and their molecular biology and genetics, and also a detailed knowledge of their nutrition. In contrast, we are still defining the anabolic and catabolic pathways for particular fatty acids, especially the polyunsaturated fatty acids (PUFA), and our understanding of PUFA enzymology, far less PUFA molecular biology and genetics, is still rudimentary. It is not surprising, therefore, that we still do not really know what constitutes desirable far less optimal dietary requirements for particular PUFA, for Homo sapiens, far less for farmed animals including fish.