Disease resistance of Pacific white shrimp, Litopenaeus vannamei, following the dietary administration of a yeast culture food supplement

A yeast culture feed supplement (Diamond V XP Yeast Culture(R), Diamond V Mills, Cedar Rapids, Iowa [IA]) was assessed for its impact on disease resistance in the Pacific white shrimp, Litopenaeus vannamei. Animals were fed a standard shrimp pellet diet supplemented with 0% (control with 1% grain carrier), 0.5% (with 0.5% carrier), or 1.0% XP daily for 4 weeks. To assess resistance to bacterial disease, at 1-week intervals 21 shrimp (0.5-2.5 g) from each test diet were injected intramuscularly with an LD50 dose (2.0 x 10(5)/g body weight) of a gram-negative shrimp pathogen, Vibrio sp. 90-69B3. Survival was monitored every 4 h for 48-h post injection. Each week, three independent bacterial challenges were performed for each diet and the results expressed as the mean percent survival +/- standard error (S.E.). A two-way analysis of variance (ANOVA) showed a significant effect of diet (p = 0.003, df= 3 1), but not duration of feeding, on survival. A one-way ANOVA showed no differences among the treatment groups after I or 2 weeks. After 3 weeks, the mean survival of 1% XP-fed shrimp (74.2 +/- 1.4%) was significantly higher than that of controls (42.9 +/- 5.5%), while mean survival of shrimp fed 0.5% XP (54.8 +/- 11.9%) was not significantly different from controls. After 4 weeks, mean survival of 1.0% XP-fed shrimp (63.4 +/- 8.8%) remained higher than that of controls but the difference was not significant (p=0.07). An insufficient number of animals were available from the 0.5% XP-fed group to perform bacterial challenges at this timepoint. Mean survival of control shrimp declined significantly over the 4 weeks of study (slope of linear regression not equal 0, p=0.005, df=11), but no decline was observed in animals fed the 0.5% or 1.0% XP diets. After 4 weeks L. vannamei fed standard shrimp pellets, 0% XP control, or 1.0% XP diets showed no significant differences in weight, suggesting that the changes in disease resistance did not correlate with changes in growth rate among the treatment groups. These results indicate that dietary administration of Diamond V XP Yeast Culture(R) can protect shrimp against a decline in resistance to bacterial disease. (C) 2004 Elsevier B.V. All rights reserved.