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 stu dy 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 immersi on in seawater were 25-35% and 30%, respectively. Semipurified diets w ith five levels of ApP (0, 20, 40, 100 and 2000 mg kg(-1) expressed as active AA were fed ad libitum to P. vannamei (PL-14 stage, mean dry w eight 0.73 mg) for 26 days. Each treatment was run in five replicates. No significant differences in growth were observed among treatments a fter 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 mu g AA.g DW-1 in corporated 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 w hen feeding more than 40 mg AA.kg diet(-1): after 1 h incubation in fr eshwater, 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 2000 mg kg(-1) group.