Vitamins are complex organic compounds required in minute amounts for normal growth, metabolism and reproduction. In extensive culture systems natural foods may be abundant enough to provide some or all essential vitamins. In intensive, high-density culture, such as heavily stocked ponds and raceways, natural foods are limited, so vitamins must be supplied in the diet to achieve normal growth. Vitamin requirements for shrimp are affected by shrimp size, age, growth rate, environmental conditions and nutrient interrelationships. There are 11 water-soluble and 4 fat-soluble vitamins believed to be required by shrimp (Akiyama et al., 1992).

Commercial shrimp feeds are usually over-fortified with expensive vitamins. Vitamin supplementation may be as high as 15% of the total ingredient cost. This over-fortification is done for several reasons. First, very little is known about vitamin requirements for shrimp. Shrimp culture generates considerable profits and the costs of over-fortification is regarded as "insurance" to maintain the quality and reputation of a feed. Second, shrimp are slow feeders and feed pellets could remain in the water for several hours. Vitamins, especially the water-soluble vitamins, will leach from the pellets. Over-fortification ensures that acceptable levels of vitamins remains in the feed. Third, vitamins are destroyed during feed processing and storage. This is especially true of ascorbic acid. The oxidation of vitamins is affected by heat, moisture, pH, the presence of certain minerals, and by lipid oxidation. Fourth, the vitamin content of feed ingredients varies. It is expensive to analyze each ingredient and each batch of ingredients, thus it is simpler to over-fortify. Lastly, ingredients may contain anti-nutritional factors which reduce or interfere with the vitamin's functions. For instance, the effect of lipid oxidation increases the requirement for vitamin E (Akiyama et al., 1992).