This vitamin C enrichment procedure has proven to be a valuable technique, especially for the evaluation of the effects of dietary vitamin C when supplemented at high levels, on for example stress resistance. However, for most species examined, the initial level of AA in Brachionus and Artemia impairs the determination of the minimal requirements for this component. Formulated diets containing variable levels of stable AA-phosphate esters were used for the determination of minimal requirements for AA in the early post-weaning stage of marine fish species (Dicentrarchus labrax, Scophthalmus maximus) and the postlarval stage of penaeid shrimp (Penaeus monodon, Penaeus vannamei). For both fish species examined results indicated that 20mg AA.kg per diet is sufficient for normal growth and survival. Requirements for production of postlarval shrimp amount to minimum 20 and 130mg AA.kg per diet, for P. monodon, resp. P. vannamei, while a level of 2000mg AA.kg per diet is needed to enhance the resistance of the shrimp postlarvae to stress conditions and bacterial infections.