The white leg Litopenaeus vannamei shrimp is of importance to the eastern Pacific fisheries and aquaculture industry but suffer from diseases such as the recently emerged early mortality syndrome. Many bacterial pathogens have been identified but the L. vannamei microbiota is still poorly known. Using a next-generation sequencing (NGS) approach, this work evaluated the impact of the inclusion in the diet of mannan oligosaccharide, (MOS, 0.5% w/w), over the L. vannamei microbiota and production behavior of L. vannamei under intensive cultivation in Ecuador. The MOS supplementation lasted for 60 days, after which the shrimp in the ponds were harvested, and the production data were collected. MOS improved productivity outcomes by increasing shrimp survival by 30%. NGS revealed quantitative differences in the shrimp microbiota between MOS and control conditions. In the treatment with inclusion of dietary MOS, the predominant phylum was Actinobacteria (28%); while the control group was dominated by the phylum Proteobacteria (30%). MOS has also been linked to an increased prevalence of Lactococcus-and Verrucomicrobiaceae-like bacteria. Furthermore, under the treatment of MOS, the prevalence of potential opportunistic pathogens, like Vibrio, Aeromonas, Bergeyella and Shewanella, was negligible. This may be attributable to MOS blocking the adhesion of pathogens to the surfaces of the host tissues. Together, these findings point to the fact that the performance (survival) improvements of the dietary MOS may be linked to the impact on the microbiota, since bacterial lines with pathogenic potential towards shrimps were excluded in the gut.

The goal of the study was to characterize the intestinal tract bacterial microbiota composition of Penaeus vannamei in intensive commercial ponds in Ecuador, comparing two shrimp-farming phases: nursery and harvest. Bacterial microbiota was examined by sequencing amplicons V2-V3 of the 16S rRNA using Ion Torrent technology. Archaea sequences were detected in both phases. Sequence analyses revealed quantitative and qualitative differences between the nursery phase and the harvest phase in shrimp intestinal microbiota composition. The main differences were observed at the phylum level during the nursery phase, and the prevailing phyla were CKC4 (37.3%), Proteobacteria (29.8%), Actinobacteria (11.6%), and Firmicutes (10.1%). In the harvest phase, the prevailing phyla were Proteobacteria (28.4%), Chloroflexi (19.9%), and Actinobacteria (15.1%). At the genus level, microbiota from the nursery phase showed greater relative abundances of CKC4 uncultured bacterium (37%) and Escherichia-Shigella (18%). On the contrary, in the microbiota of harvested shrimp, the prevailing genera were uncultured Caldilinea (19%) and Alphaproteobacteria with no other assigned rate (10%). The analysis of similarity ANOSIM test (beta diversity) indicated significant differences between the shrimp microbiota for these two farming phases. Similarly, alfa-diversity analysis (Chao1) indicated that the microbiota at harvest was far more diverse than the microbiota during the nursery phase, which showed a homogeneous composition. These results suggest that shrimp microbiota diversify their composition during intensive farming. The present work offers the most detailed description of the microbiota of P. vannamei under commercial production conditions to date.

RESUMEN.Los prebióticos tienen el potencial de incrementar la eficiencia y sostenibilidad de la producción acuícola. Uno de los prebióticos más promisorios en acuicultura son los Manano oligosacáridos (MOS). Estos MOS son moléculas de carbohidratos complejos derivados de la pared de la célula de la levadura Saccharomyces cerevisiae, que impiden la adhesión de patógenos bacterianos porque actúan bloqueando la adherencia de las lectinas microbianas con los carbohidratos presentes en la superficie de las células intestinales. Esta prevención de la adhesión impide la colonización y proceso infectivo de los patógenos. La ventaja del uso de MOS es que puede prevenir infecciones a través de mecanismos diferentes a los utilizados por los antibióticos. Este artículo muestra los avances obtenidos en uso de MOS como prebióticos en la acuicultura, en particular en el cultivo de crustáceos, donde han generado respuestas positivas en todas las experiencias actuando sobre el incremento del crecimiento, la supervivencia, modulando la respuesta inmune y modificando la morfología del tracto digestivo. La identificación de las cepas que son promovidas o excluidas y la caracterización de la acción moduladora en la microbiota resultante quedan abiertas como uno de los campos a desarrollar en conjunto con la extensión de estos resultados a la práctica productiva. Palabras clave: crustáceos, manano oligosacáridos, MOS, prebióticos, microbiota, crecimiento. Mannan oligosaccharides as prebiotics in crustacean aquacultureABSTRACT. Probiotics have the potential to increase the efficiency and sustainability of aquaculture production. The mannan-oligosaccharides (MOS) are complex carbohydrates derived from the cell wall of the yeast Saccharomyces cerevisiae, which act by blocking adherence of bacterial lectins to carbohydrates on the surface of intestinal cells; this action prevents colonization and infection processes carried out by bacterial pathogens. In this work, we review the current evidence about the use of MOS as prebiotics in shellfish aquaculture, enlightening the positive responses in most of the experiences, such as improvement in growth and survival, modulating the immune response and modifying the morphology of the digestive tract. The identification of strains that are promoted or excluded, and the characterization of the resulting modulating action in gut´s microbiota, remains open as one of the fields to be developed in conjunction with the extension of these results to the productive practice.