ESSENTIAL FATTY-ACID REQUIREMENT OF THE CHINESE PRAWN, PENAEUS-CHINENSIS

The aim of this study was to determine the essential fatty acid (EFA) requirement of one of the most important commercially cultured crustacean species in the world, Penaeus chinensis. Groups of 16 individually housed juvenile Chinese prawn were fed for 60 days with 12 semi-purified experimental diets. These diets were based on the crab-protein-concentrate Standard Reference Diet and contained either 5% of a mixture of tripalmitin (16:0) and triolein (18:1n-9) (EFA deficient control diet), or 4% of this mixture and a 1% supplement of various purified polyunsaturated fatty acids (PUFA) or highly unsaturated fatty acids (HUFA). Prawns fed the EFA-deficient control diet suffered 100% mortality. The prawns fed a diet containing 1% trilinolenin (18:3n-3) had higher growth and longer survival than that of animals fed the diet containing 1% trilinolein (18:2n-6). Feeding a diet containing a mixture 0.5% of each of these lipids resulted in a greater growth rate and a 0.25:0.75 mixture of trilinolein and trilinolenin produced a greater survival than any other mixture or either purified fatty acid supplement alone. When the 18-carbon polyunsaturated fatty acid supplement was replaced with 1% of the triglyceride of arachidonic acid in the diet fed to prawns, however, the growth was about equal to that of prawns receiving 1% 18:3n-3 and survival was significantly higher than that of prawns fed any combination of 18:2n-6 or 18:3n-3 tested, while being less than that of prawns fed a diet containing 1% of the triglyceride of docosahexaenoic acid (DHA, 22:6n-3). The prawns fed the EFA-deficient control diet or any of the diets with 18:2n-6 or 18:3n-3 supplemented individually had extremely low body lipid levels. Mixtures of these two fatty acids or any combination of the n-6 or n-3 HUFA resulted in more normal body lipid levels, suggesting that both n-3 and n-6 type fatty acids might be required by the Chinese prawn. The fatty acid composition of the total body lipid reflected that of the experimental diets. Though 18:2n-6 and 18:3n-3 were not apparently desaturated and elongated to the physiologically important EFA members of the respective n-6 and n-3 series of fatty acids (20:4n-6, 20:5n-3 and 22:6n-3), there was evidence for elongation of these acids to 20:2n-6 and 20:3n-3. The results indicate that the essential fatty acid values of the fatty acids in the diet of the Chinese prawn increased in the following order 18:2n-6 < 18:3n-3 < 20:4n-6 < 22:6n-3.