Improved production of postlarval white shrimp through supplementation of L-ascorbyl-2-polyphosphate in their diet

L-ascorbyl-2-polyphosphate (ApP) was used as a vitamin C source to study the ascorbic acid (AA) requirements for the early postlarval stages of white shrimp (Penaeus vannamei). First the stability of ApP in the diets was determined: ApP losses after pelletizing and 10 min immersion in seawater were 25-35% and 30%, respectively. Semipurified diets with five levels of ApP (0, 20, 40, 100 and 200 mg kg-1 expressed as active AA were fed ad libitum to P. vannamei (PL-14 stage, mean dry weight 0.73 mg) for 26 days. Each treatment was run in five replicates. No significant differences in growth were observed among treatments after 26 days of feeding. As of day 19 of feeding, increased mortality was observed for shrimp fed diets supplemented with 0, 20, 40 and 100 mg AA.kg diet-1, which was caused by a Vibrio harveyi infection. The highest level of dietary AA, corresponding with 200 µg AA.gDW-1 incorporated in the body tissue, appeared to be sufficient to obtain an optimal resistance to the bacterial infection. Moreover, a significant effect of dietary AA on the stress resistance (measured by means of a salinity shock) of the postlarval shrimp (PL-41 stage) was observed when feeding more than 40 mg AA.kg diet-1: after 1h incubation in freshwater, 62.5% and 32.5% of the shrimp fed 40 and 0 mg AA.kg diet-1, respectively, survived the osmotic stress, while only 10% mortality was noticed in the 2,000 mg kg-1 group