The incorporation of various nutrients at levels in excess of nutritional requirements in animal diets has been shown to enhance immunity and disease resistance in several species. One hypothesis relating to the enhancement phenomenon suggests that the presence of certain key nutrients above maintenance levels provides a readily available reservoir for use by the host defense system upon activation of that system. High density and unpredictable environmental factors associated with mariculture produce stress and an increased susceptibility to disease organisms.

Among the nutrients which have been shown to effectively enhance immunity and disease resistance is Vitamin C. Vitamin C deficiencies have caused reduced growth rate, deformation of skeletal and cartilaginous tissues of fish, capillary fragility, slow wound repair, melanized hemocytic lesions in shrimp and increased rate of mortality.

This is a report of a study utilizing a purified diet in evaluating Vitamin C effects on histopathology of tissues of post larval shrimp (Penaeus vannamei). The study was conducted utilizing 20-liter circular tanks in a recirculating system. The dietary effects of selected vitamin C levels were evaluated in terms of pathologic changes observed in the shrimp tissues. The findings were characterized by melanized hemocytic lesions distributed throughout the collagenous tissues of the shrimp. It has been reported that high and deficient levels of certain nutrients can reduce immune function. This preliminary study showed that, in the presence of bacterial stress, shrimp that received no vitamin C and shrimp that received a high level of vitamin C produced the highest number of pathologic lesions.