EFFECT OF VDS FEED ADDITVE MIX ON THE RESISTANCE OF L. vannamei TO WSSV

Lodewijk Rosseel*, Koen Blanchaert
VDS nv
Paanderstraat 40
Deerlijk, 8540
koen@vds-afs.be
 

The present trial aimed to evaluate if L. vannamei shrimp, which were subjected to a feeding trial with specific dietary treatments (see Paper "Effects of VDS feed additive mix on the growth performance of L. vannamei"), showed an improved resistance to WSSV infection. This was based on the assumption that the experimental diets contained a specific freed additive mix that can improve shrimp health in general and/or stimulate (antiviral) immunity specifically.

In order to evaluate the resistance to WSSV, 20 shrimp per treatment were orally inoculated (natural infection route) with 108.3SID50 (shrimp infectious doses 50% endpoint) WSSV solid inoculum  under standard laboratory conditions. Three days before starting the WSSV challenge, shrimp were transferred from the feeding trial facility of VDS to the disease challenge facility of IMAQUA. The shrimp were housed individually in 10L glass tanks (infection units). Aside the negative control (CTRL) and the 3 different dietary treatments of VDS (A,B,C), an internal IMAQUA (commercial) control (ICTRL) was also included in the evaluation (Tabel 1). The clinical outcome of the WSSV challenge test was evaluated by the following parameters: Cumulative percentage of mortality by day 7; Cumulative percentage of diseased shrimp by day 7; Onset of mortality; Cessation of mortality.

Although we can see an improved survival in treatment B when compared to the CTRL (Tabel 1), this difference was not statistically significant. This was much probably originated by the low mortality outcome and a limited sample size (number of shrimp per dietary treatment). It could be expected that at a higher mortality level using younger animals and with a higher sample size (+35 animals) per treatment, this difference would turn out to be significant. The difference in mortality between B and ICTRL were statistically significant. This reinforces the assumption that treatment B can induce a higher resistance of shrimp to WSSV.