The aquaculture industry is continuously interested in innovative practices with the aim of improving farm practices while ensuring sustainable development. This is reflected in a global demand for quality shrimp and a better environment. One of the key strategic priorities is to improve water quality by reducing organic matter in ponds. Organic matter is the source of ammonia, nitrite, nitrate and hydrogen sulfide for pathogen development. The Bacillus strains are known for their high levels of enzymes that are able to degrade organic matter, colonize the water column and therefore to reduce the bacterial load and consequently improve shrimp health. In this study, we evaluate the potential of marine probiotics as bioremediators and in feed supplementation but above all their resistance capacity against a Vibrio parahaemolyticus infection by reducing shrimp mortality and their impact on larvae and water microbiota.
A 7-week supplementation with a bacteria consortium added in water was performed in 800-liter ponds (n=1000, water temperature = 28°C) in triplicate on Litopenaeus vannamei PL-12 . The physico-chemical parameters, mortality and weight were monitored during the supplementation phase. Larvae were then transferred in smaller ponds of 40L (n=60, 3 replicates) prepared during 2 days by inoculating water probiotics and challenged for 15 days with a Vibrio parahaemolyticus causing acute hepatopancreatic necrosis disease (AHPND). The capacity of the bacteria consortium composed of three Bacillus strains on lithotamne support on shrimp survival rate was evaluated and demonstrated a survival rate improvement of +50% at the end of the challenge test compared to the control who did not receive probiotic supplementation. A metagenomic analysis was done by metabarcoding on water during the supplementation phase to see the impact of the probiotic on the composition of sea water. Aquatic probiotics can also have an impact on the microbiota’s gut through the ingestion of water and organic matter by shrimp larvae. The variation in the microbiota gut composition was also analyzed . The results show the ability of the probiotic to colonize the water column and influence the surrounding microbiota. Metagenomic analyses were also done on dead and alive challenged larvae and a smaller quantity of the Vibrio family was found with a colonization of probiotic bacteria. This study demonstrated the ability of marine probiotics added to water ponds to help shrimp larvae fight against stress caused by V. parahaemolyticus .