EFFECT OF VITAMIN-C AND ASTAXANTHIN ON STRESS AND DISEASE RESISTANCE OF POSTLARVAL TIGER SHRIMP, PENAEUS-MONODON (FABRICIUS)

Postlarvae of tiger shrimp, Penaeus monodon (Fabricius), were fed semi purified diets supplemented with various levels of astaxanthin (AX) an d ascorbic acid-polyphosphate (ApP): three groups were fed 230 mg AX k g(-1) diet combined with 100, 1700 and 3400 mg ascorbic acid (AA) kg(- 1) diet, respectively; two diets contained 810 mg AX kg(-1) mixed with 200 and 1700 mg AA kg(-1), respectively. Each treatment was run in fo ur replicates. Incorporated levels of AA and AX, production output, an d physiological condition were recorded after 4 weeks of feeding. Whol e-body AA (21-47 mu g g(-1)) and AX concentrations (19-35 mu g g(-1)) were linked to dietary ApP and AX supply, respectively, although not s ignificantly for the latter. The biomass of the group receiving the lo wer dietary ApP-AX combination was significantly lower than for all ot her treatments, i.e. 3.1 versus 3.9 g, respectively In the groups fed 230 mg AX kg(-1) diet, significant differences in stress resistance we re observed according to the dietary ApP level, i.e. raising the vitam in C content in the feed from 100 to 3400 mg AA kg(-1) resulted in a c oncomitant drop in mortality after an osmotic shock. For the treatment s receiving 810 mg AX kg(-1) diet, the beneficial effect of extra diet ary vitamin C was not significant. An increase in the dietary AX for s hrimp fed comparable ApP levels resulted in a significant drop of the stress index from 56 to 33 (cumulative mortality index). An increased resistance to salinity shock was demonstrated in association with supp lementation of high dietary AA or AX levels. No conclusive results reg arding possible improved disease resistance could be made since no mor tality was observed after a disease challenge with Vibrio harveyi.