Fish are a rich source of long-chain n-3 (omega-3) polyunsaturated fatty acids (PUFA), essential nutrients that have important structural and physiological roles in several body systems, including neurological, immune, and cardiovascular. Because humans cannot synthesize n-3 PUFA, these nutrients must be consumed in the diet. Conversion from the parent n-3 PUFA, α-linolenic acid, to the more biologically active long-chain n-3 PUFA, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), is inefficient and therefore consumption of some preformed long-chain n-3 PUFA is important for optimal health. In the United States and elsewhere, fish is the main dietary source of DHA and EPA.