The major functions of essential fatty acids are related to their roles as components of phospholipids and as precursors of prostaglandins. Essential fatty acids are found in the highest concentration in phospholipids and, as such, are important in maintaining the flexibility and permeability of biological membranes, in lipid transport, and in activation of certain enzymes. As precursors of prostaglandins they are probably involved in many diverse physiological and metabolic functions (Akiyama et al., 1992).

Four fatty acids are considered essential for shrimp: linoleic (18:2n6), linolenic (18:3n3), eicosapentacnoic (20:5n3, EPA) and decosahexacnoic (22:6n3, DHA). In general, plant oils are high in 18:2n6 and 18:3n3, while the marine animal oils are high in 20:5n3 (EPA) and 22:6n3 (DHA). Saturated fats, such as lard and tallow, are not suitable supplements in shrimp feeds (Akiyama et al., 1992).