REDUCING EARLY IMPACT ON SHRIMP OF WHITE SPOT SYNDROME VIRUS IN FIELD CONDITIONS

White Spot Syndrome Virus (WSSV) is a highly contagious dsDNA virus causing an annual loss of one billion US dollars to the shrimp industry by infecting the digestive tract and other tissues of Penaeid shrimps. It has been proved that Copper-Echanged Clay (CeC), an ion activated clay, has a high antimicrobial potency on various pathogens, but the effect of CeC on aquatic viral pathogens has never been proved. Therefore, a trial was performed at Incabiotech ConceptoAzul (Peru) to assess the effect of CeC on L. vannamei during a mild White Spot Syndrome Virus challenge mimicking field conditions

A smooth WSSV challenge was applied to L. vannamei juveniles during 6 weeks in 15-liter tanks containing 100 PL/tank. Two inoculations were performed at week 1 and week 4 with an inoculum prepared from a biomass of infected live shrimp positive for WSSV at second PCR. Three groups were implemented: negative control group (no inoculation), positive control group (WSSV inoculation) and CeC group (WSSV inoculation and 5kg/ton CeC coated on the feed). Differences in survival rates between the negative and positive control groups did not exceed 13 points and all dead shrimps were positive at the second PCR analysis, demonstrating that the challenge mimics real field conditions in which the virus develops slowly but is lethal to weaker animals.

Figure 1 illustrates the survival rate of the different treatments. The group fed with CeC showed a survival rate 15 points higher than in the positive control group. CeC significantly improved survival of shrimps, even in comparison to the non-inoculated control group.

Figure 2 illustrates the tank biomass and shows that shrimp fed with the CeC had a much higher growth than the control at the end of the trial, confirming the growth promoter effect of CeC.

The positive results observed suggest that Copper Exchanged Clay (CeC) is an effective solution to reduce the early development of WSSV, therefore also preventing WSSV massive outbreaks. A significant higher survival rate was observed associated to a beneficial effect on growth of juvenile shrimps, which tends to validate the protective effect of CeC against a viral pathogen such as WSSV.