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Microbial communities, mainly those with probiotic characteristics, positively affect the culture of diverse organisms, including shrimp. In this study, three diets containing different types of probiotics were evaluated on the composition and diversity of the microbial community in the water column and gut of Litopenaeus vannamei, as well as on the expression of genes related to the immune system and resistance of the organisms after being challenged with WSSV and Vibrio parahaemolyticus. Results showed that probiotics affected the microbial community structure in water and shrimp. The expression of beta-glucan binding protein and prophenoloxidase increased in the treatments with probiotics compared to the control before and after the challenge. Overall the survival of shrimp was higher in all the treatments than in control. Results suggest that using probiotics in BFT systems could provide an extra benefit for these kinds of systems.

The aim of this work was to study the functional properties of bacterial communities in shrimp-culture bioflocs produced with amaranth (BFT_Amaranth) and wheat (BFT_Wheat) as biofloc promoters. No significant differences between treatments were recorded for physical and chemical parameters of water. A total of 22 phyla were detected in the biofloc samples, but the taxonomic structure was based on four principal phyla (Planctomycetes, Proteobacteria, Bacteroidetes, and Firmicutes). Most of the predicted KEGG pathways of bacterial communities contained in both bioflocs were associated with metabolism (50–53%), genetic information processing (19–21%), environmental information processing (12–15%), cellular processes and signaling (4–6%), organismal systems (1–2%) and other (3–5%). Both, the taxonomic and functional profiles of the two bioflocs were different at the beginning of the trial, but similar at the end of it, suggesting that the micro-environmental conditions of the culture units shaped the microbiota of biofloc regardless the type of seed used. Evidence of methane (RuMP and Serine pathways) and nitrogen (via N fixation, denitrification, nitrification, and detoxification) metabolism was detected in both BFT_Amaranth and BFT_Wheat, regardless of the sampling date. Carbon dioxide fixation was also detected, including photosynthetic pathways such as the Calvin cycle; however, other carbon dioxide fixation pathways including the reductive citric acid cycle, dicarboxylate-hydroxybutyrate cycle, 3-hydroxypropionate-bicycle and the Wood-Ljungdahl pathway were detected in both bioflocs. These results represent a first insight into the functions exerted by bioflocs in aquacultural systems, and suggest that nitrogenous and carbonaceous compounds can be simultaneously processed through diverse pathways by bacteria thriving in bioflocs.

The taxonomy profiles of bacterial communities contained in bioflocs produced with amaranth (BFT_Amaranth) and wheat (BFT_Wheat) grains as substrates, and used for shrimp culture were evaluated. The proliferation of heterotrophic bacteria was promoted by maintaining a carbon:nitrogen ratio of 12:1. High throughput sequencing of the 16S-rRNA gene revealed that the maximum difference between BFT_Amaranth and BFT_Wheat was registered at the beginning of the trial, when BFT_Wheat was dominated by Bacteroidetes (80–85%), whereas BFT_ Amaranth was dominated by Planctomycetes (42%), Proteobacteria (26%) and Bacteroidetes (16%). However, the taxonomic profile of both biofloc types were similar at the end of the trial, suggesting that the type of substrate affected the initial biofouling process, but the similar physicochemical conditions maintained during the trial favored the same heterotrophic communities in both treatments; herein, only 97 were shared between BFT_Wheat and BFT_Amaranth at the beginning of the trial, but 185 at the end. Thereafter, a better productive response in terms of survival, growth rate and FCR was registered for shrimp reared with BFT_Wheat, which corresponded to the biofloc registering the highest protein content at the end of the trial (18.5%), compared to BFT_Amaranth (12.7%). Finally, despite the high similarity detected among both biofloc types, this may not be strongly associated with their nutritional composition, nor the massification rate of these microbial communities.

Even though Litopenaeus vannamei is one of the most important species used in aquaculture, little is known about the functions provided by the intestinal microbiota for host development. This study aims to determine the taxonomic and functional changes in the L. vannamei gut microbiota during postlarval development in a recirculation system under controlled conditions for 80 days. The results revealed that the Vibrionaceae family predominated at the beginning of the experiment, when the postlarvae weighed 0.5 to 1.5 g. The representativeness of the family Rhodobacteraceae increased to the detriment of Vibrionaceae, which showed a constant decrease as the shrimp reached the juvenile and adult stages. Finally, the Intrasporangiaceae family remained constant in postlarvae weighing 4 to 10 g. Differences in the taxonomic profile at the family level between culture days were observed through principal component analysis (PCA), where two main clusters were observed: a group of microbiota sampled at 0 D and 20 D and another of samples collected at 40 D, 60 D and 80 D, suggesting that the microbiota tend to be variable during the first postlarval phase but become more constant towards the adult phase. Microbial-mediated functions predicted by PICRUSt showed an overall functional redundancy, suggesting that gut conditions maintain the same microbiota functions regardless of changes in the taxonomic structure. These results also suggest that shrimp are under certain selective pressure favoring microbiota with specific functions according to their requirements.

The physiological and immune responses of adult shrimp (Litopenaeus vannamei) undergoing the acute phase of the necrotizing hepatopancreatitis (NHP) disease and the efficiency of oxytetracycline (OXI) and florfenicol (FF) to eliminate the pathogen were evaluated. Four shrimp groups were considered: three groups infected with necrotizing hepatopancreatitis bacteria (NHP-B) (two treated with antibiotics and a positive control) and one group non-infected (negative control). Hemolymph concentration of glucose, lactate, acylglycerides, cholesterol, total protein, aminotransferases, superoxide dismutase, and the transcriptional expression of several immune related genes were monitored at the acute phase of the disease, and at 15 and 20 days after administration of antibiotics (daa). Shrimp from the positive control registered a mortality of 100%. NHP-B infection affected the immu-nophysiological response of shrimp; herein, most of the parameters were significantly up regulated in infected shrimp before the use of antibiotics, compared to the negative control. Increased transcriptional levels of clotting protein, lipopolysaccharide and β-1-3-glucan binding protein (LGBP), serine protease, peroxinectin, lysozyme, heat shock proteins (HSP) 60 and 70 were detected in shrimp treated with OXI. At 20 daa NHP-B was still detected in FF-treated shrimp, but not in OXI-treated shrimp. It is hypothesized that despite none of the antibiotics per se eliminated the bacterium, both had a negative effect on its virulence. OXI seems to have a greater effect, allowing shrimp to integrate a better immune response at 15 daa.