Essential fatty acids in fish physiology.

This paper emphasizes those aspects of fatty acid research in fish that have relevance to the investigation of the functions of essential fatty acids in other species. Lipid requirements of fish came under investigation only in the 1960s. The most significant finding has been the requirement for n-3 fatty acids. The dietary ratio of (n-3):(n-6) is critical if the essential requirement is met by C18 fatty acids because of competition between fatty acids for the enzymes involved in elongation and desaturation to produce the physiologically essential long-chain fatty acids. The fatty acid composition of fish lipids varies according to the fatty acid profile of the dietary lipid. The fatty acid composition of fish also responds to temperature changes in an adaptive mechanism for maintenance of membrane homeoviscosity and physiological function over a range of temperatures. The dietary intake of essential fatty acids by brood stock must be adequate for ova formation and for embryonic development, with the latter requirement being more critical for reproductive success. Absolute requirements of fish for essential fatty acids are difficult to define and may vary depending upon the dietary ratio of (n-3) to (n-6) fatty acids.