Ascorbic acid is structurally one of the simplest vitamins. Ascorbic acid is soluble in water and ethyl alcohol but insoluble in most organic solvents. It is an important antioxidant and is easily oxidized. The principle function of ascorbic acid is in the formation of collagen, an essential component of capillaries and connective tissues. Ascorbic acid is also involved in the synthesis of steroid hormones. Deficiency symptoms include "Black Death", a disease characterized by melanized haemocytic lesion in collagenous tissues, problems with or decreased rate of molts, a lighter colored hepatopancreas, reduced growth and mortality (Akiyama et al., 1992).

Ascorbic acid is rapidly oxidized during feed storage and feed processing. The ascorbic acid loss in stored feeds is approximately 50% per month. Unprotected forms of ascorbic acid should not be used in feeds because 70% - 90% will be destroyed during feed processing. Coated forms of ascorbic acid (silicone, gelatin) are marginally better. Destruction of coated ascorbic acid during feed pelleting and extrusion would range from 30% - 50% and 50% - 80%, respectively. Two heat-stable ascorbic acid derivatives, L-ascorbyl-2-polyphosphate and L-ascorbyl-2-phosphate magnesium have been recently introduced. These ascorbic acid derivatives are utilized by shrimp, relatively stable during feed processing with only 20% destroyed, and stable during feed storage with 20% loss over 6 months. Another ascorbic acid derivative, L-ascorbyl-2-sulfate, is heat stable but its utilization by shrimp has not been demonstrated (Akiyama et al., 1992).

The requirement of ascorbic acid by shrimp is 50 - 80 mg/kg. However, ascorbic acid supplementation levels in shrimp feed will vary due to the form of ascorbic acid, processing conditions and feed storage time. Recommended supplementation level of coated ascorbic acid and the stable ascorbic acid derivatives are 1,000 mg/kg and 100 mg/kg, respectively (Akiyama et al., 1992).