GUT MICROBIATA AND HISTOPATHOLOGICAL CHANGES ASSOCIATED WITH WFD IN JUVENILES Litopenaeus vannamei AND THE MODULATING EFFECT OF A MULTI-STRAINS YEAST FRACTION PRODUCT

White Feces Syndrom (WFS) is a widespread digestive disease of farmed shrimp causing severe economic losses across Asia. Recent works have confirmed the infectious nature of the disease (Tran, 2017) and documented a marked shift in the intestinal microbial community of clinically diseased shrimp (Hou et al., 2018) exhibiting severe damages of the HP and mid-gut (Sriurairatana et al., 2014). The aim of the trial was to assess the potential of a novel multi-strains yeast fraction product (MsYF) against WFD-induced intestinal microbial shift, histopathological damage and performance loss.

The trial lasted 26 days with a standardized per os WFS-challenge at day 14 using juvenile whiteleg shrimp (0.75g; 30 shrimp/tank) with a total of 3 test groups and 8 replicate / group (24 tanks of 120L). The trial tested the effect of supplementation with MsYF at 1 kg/T of feed (Lallemand SAS, Blagnac, France) against a positive (challenged) and a negative (not challenged) control fed the non-supplemented diet. For gut microbiota and histopathological assessment of the gastrointestinal-tract, 3 shrimp/group were sampled immediately prior and 48h after the WFS-challenge corresponding to the peak of mortality.

Results indicate a better maintenance of the crop performance and a lower severity of the WFS outbreak associated with clear benefits of MsYF on GI-tract histopathology. Two days after the challenge, intestinal α-diversity indexes were not affected but the β-diversity shifted and was more consistent between shrimps indicating shaping of the gut microbiota by the infectious agent. In particular, the relative abundance of Shewanella sp. and Tenacibaculum sp. but not Vibrio sp. was markedly increased at the expense of more minor but expected beneficial genus. The test compound increased the consistency of intestinal microbial diversity prior and after the challenge with, in particular, a reduction in the relative abundance of Vibrio sp.

The shift in intestinal microbiota documented here under a controlled WFS-challenge suggests a role of the commensal microbiota in the pathogenesis of the WFS. The study raise credible hypothesis on the etiology of the disease and highlights the potential of reinforcing the intestinal microbiota equilibrium against Vibrio sp. induced disruption that could mediate WFS.