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Postlarvae of tiger shrimp, Penaeus monodon (Fabricius), were fed semipurified diets supplemented with various levels of astaxanthin (AX) and ascorbic acid-polyphosphate (ApP): three groups were fed 230 mg AX kg -1 diet combined with 100, 1700 and 3400 mg ascorbic acid (AA) kg -1 diet, respectively; two diets contained 810 mg AX kg -1 mixed with 200 and 1700 mg AA kg -1 , respectively. Each treatment was run in four replicates. Incorporated levels of AA and AX, production output, and physiological condition were recorded after 4 weeks of feeding. Whole-body AA (21-47 µg g -1 ) and AX concentrations (19-35 µg g -1 ) were linked to dietary ApP and AX supply, respectively, although not significantly for the latter. The biomass of the group receiving the lower dietary ApP-AX combination was significantly lower than for all other treatments, i.e. 3.1 versus 3.9 g, respectively. In the groups fed 230 mg AX kg -1 diet, significant differences in stress resistance were observed according to the dietary ApP level, i.e. raising the vitamin C content in the feed from 100 to 3400 mg AA kg -1 resulted in a concomitant drop in mortality after an osmotic shock. For the treatments receiving 810 mg AX kg -1 diet, the beneficial effect of extra dietary vitamin C was not significant. An increase in the dietary AX for shrimp fed comparable ApP levels resulted in a significant drop of the stress index from 56 to 33 (cumulative

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Native and two modified forms of soybean phosphatidylcholine were used to study the nutritional effect of their fatty acids for postlarval Penaeus japonicus. Five semipurified and isolipidic diets were formulated using casein as a protein source. Three diets contained 1.5% of different types of phosphatidylcholine (95% purity), i.e. native soybean phosphatidylcholine, hydrogenated soybean phosphatidylcholine and 1-acyl lyso soybean phosphatidylcholine, besides 1% of n-3 highly unsaturated fatty acid formulated as triglycerides. Two negative control diets contained either triglycerides or ethyl esters as a source of n-3 highly unsaturated fatty acids without phospholipid. The experiment was conducted during two successive phases of 20 d starting from 12-d old postlarvae. Feeding the diet containing native soybean phosphatidylcholine resulted in significantly better growth and resistance to osmotic shock of P. japonicus postlarvae compared to the other diets. The total lipid content of the tissue was significantly increased by the supplementation of soybean phosphatidylcholine, whereas no significant difference was observed for the shrimp fed the modified phosphatidylcholine sources compared to the phosphatidylcholine-free diet at the end of the experiment. Shrimp fed the diet containing soybean phosphatidylcholine exhibited a higher polar lipid fraction in the whole body total lipid mainly as a result of the increased proportion of phosphatidylcholine and to a lesser extent of phosphatidylinositol at the expense of free fatty acids, free sterols and sterol esters. The content of 20:5n-3, 22:6n-3 and total n-3 highly unsaturated fatty acids in the shrimp tissue were higher in shrimp fed the native soybean and hydrogenated soybean phosphatidylcholine diets compared to those fed the phosphatidylcholine-free and 1-acyl lyso soybean phosphatidylcholine-based diets. The fatty acid profile of tissue phosphatidylethanolamine was more influenced by the type of dietary phosphatidylcholine than that of tissue phosphatidylcholine. In the absence of phospholipids in the diet, triglyceride fish oil and a mixture of ethyl ester concentrate and coconut oil with similar n-3 highly unsaturated fatty acids content were equivalent sources of n-3 highly unsaturated fatty acids. The beneficial effects of dietary phospholipids may be due to a more efficient transport and utilization of dietary neutral lipids through a better lipid mobilization following absorption in the intestinal mucosa rather than due to a better emulsification of neutral lipid in the gut lumen. The functionality of phosphatidylcholine in the diet of postlarval P. japonicus requires the presence of unsaturated fatty acids and an intact fatty acid moiety.